pgsql: ECPG only copied #include statements instead of processing them

Log Message:
-----------
ECPG only copied #include statements instead of processing them according to
commandline option "-i". This change fixes this and adds a test case. It also
honors #include_next, although this is probably never used for embedded SQL.

Modified Files:
--------------
pgsql/src/interfaces/ecpg/preproc:
pgc.l (r1.172 -> r1.173)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/preproc/pgc.l?r1=1.172&r2=1.173)
pgsql/src/interfaces/ecpg/test/compat_informix:
rnull.pgc (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/compat_informix/rnull.pgc?r1=1.2&r2=1.3)
test_informix.pgc (r1.6 -> r1.7)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/compat_informix/test_informix.pgc?r1=1.6&r2=1.7)
pgsql/src/interfaces/ecpg/test/expected:
compat_informix-rnull.c (r1.17 -> r1.18)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/compat_informix-rnull.c?r1=1.17&r2=1.18)
compat_informix-test_informix.c (r1.21 -> r1.22)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/compat_informix-test_informix.c?r1=1.21&r2=1.22)
preproc-strings.c (r1.3 -> r1.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/preproc-strings.c?r1=1.3&r2=1.4)
preproc-strings.stderr (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/expected/preproc-strings.stderr?r1=1.4&r2=1.5)
pgsql/src/interfaces/ecpg/test/preproc:
Makefile (r1.7 -> r1.8)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/preproc/Makefile?r1=1.7&r2=1.8)
strings.pgc (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/preproc/strings.pgc?r1=1.2&r2=1.3)

Added Files:
-----------
pgsql/src/interfaces/ecpg/test/preproc:
strings.h (r1.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/test/preproc/strings.h?rev=1.1&content-type=text/x-cvsweb-markup)