pgsql: Add E'' syntax so eventually normal strings can treat backslashes

Log Message:
-----------
Add E'' syntax so eventually normal strings can treat backslashes
literally.

Add GUC variables:

"escape_string_warning" - warn about backslashes in non-E strings
"escape_string_syntax" - supports E'' syntax?
"standard_compliant_strings" - treats backslashes literally in ''

Update code to use E'' when escapes are used.

Modified Files:
--------------
pgsql/contrib/tsearch2/expected:
tsearch2.out (r1.11 -> r1.12)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tsearch2/expected/tsearch2.out.diff?r1=1.11&r2=1.12)
pgsql/contrib/tsearch2/sql:
tsearch2.sql (r1.7 -> r1.8)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tsearch2/sql/tsearch2.sql.diff?r1=1.7&r2=1.8)
pgsql/doc/src/sgml:
runtime.sgml (r1.330 -> r1.331)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/runtime.sgml.diff?r1=1.330&r2=1.331)
syntax.sgml (r1.100 -> r1.101)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/syntax.sgml.diff?r1=1.100&r2=1.101)
pgsql/src/backend/parser:
scan.l (r1.125 -> r1.126)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/scan.l.diff?r1=1.125&r2=1.126)
pgsql/src/backend/utils/misc:
guc.c (r1.268 -> r1.269)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.268&r2=1.269)
postgresql.conf.sample (r1.147 -> r1.148)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample.diff?r1=1.147&r2=1.148)
pgsql/src/bin/initdb:
initdb.c (r1.85 -> r1.86)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/initdb/initdb.c.diff?r1=1.85&r2=1.86)
pgsql/src/bin/pg_dump:
pg_dumpall.c (r1.61 -> r1.62)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dumpall.c.diff?r1=1.61&r2=1.62)
pgsql/src/bin/psql:
describe.c (r1.117 -> r1.118)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/describe.c.diff?r1=1.117&r2=1.118)
pgsql/src/include/catalog:
pg_proc.h (r1.370 -> r1.371)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.370&r2=1.371)
pgsql/src/include/utils:
guc.h (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h.diff?r1=1.60&r2=1.61)
pgsql/src/test/regress/expected:
arrays.out (r1.25 -> r1.26)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/arrays.out.diff?r1=1.25&r2=1.26)
copy2.out (r1.21 -> r1.22)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/copy2.out.diff?r1=1.21&r2=1.22)
int8.out (r1.9 -> r1.10)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/int8.out.diff?r1=1.9&r2=1.10)
numeric.out (r1.16 -> r1.17)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/numeric.out.diff?r1=1.16&r2=1.17)
rowtypes.out (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/rowtypes.out.diff?r1=1.2&r2=1.3)
timestamp.out (r1.27 -> r1.28)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamp.out.diff?r1=1.27&r2=1.28)
timestamptz.out (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamptz.out.diff?r1=1.17&r2=1.18)
type_sanity.out (r1.25 -> r1.26)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/type_sanity.out.diff?r1=1.25&r2=1.26)
pgsql/src/test/regress/input:
copy.source (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/input/copy.source.diff?r1=1.12&r2=1.13)
pgsql/src/test/regress/output:
copy.source (r1.10 -> r1.11)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/output/copy.source.diff?r1=1.10&r2=1.11)
pgsql/src/test/regress/sql:
arrays.sql (r1.20 -> r1.21)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/arrays.sql.diff?r1=1.20&r2=1.21)
copy2.sql (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/copy2.sql.diff?r1=1.12&r2=1.13)
int8.sql (r1.7 -> r1.8)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/int8.sql.diff?r1=1.7&r2=1.8)
numeric.sql (r1.11 -> r1.12)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/numeric.sql.diff?r1=1.11&r2=1.12)
rowtypes.sql (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/rowtypes.sql.diff?r1=1.2&r2=1.3)
timestamp.sql (r1.13 -> r1.14)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/timestamp.sql.diff?r1=1.13&r2=1.14)
timestamptz.sql (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/timestamptz.sql.diff?r1=1.6&r2=1.7)
type_sanity.sql (r1.25 -> r1.26)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/type_sanity.sql.diff?r1=1.25&r2=1.26)