pgsql: Add some debug support code to try to catch future mistakes in

Log Message:
-----------
Add some debug support code to try to catch future mistakes in the area of
input functions that include garbage bytes in their results. Provide a
compile-time option RANDOMIZE_ALLOCATED_MEMORY to make palloc fill returned
blocks with variable contents. This option also makes the parser perform
conversions of literal constants twice and compare the results, emitting a
WARNING if they don't match. (This is the code I used to catch the input
function bugs fixed in the previous commit.) For the moment, I've set it
to be activated automatically by --enable-cassert.

Modified Files:
--------------
pgsql/src/backend/parser:
parse_type.c (r1.94 -> r1.95)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_type.c?r1=1.94&r2=1.95)
pgsql/src/backend/utils/mmgr:
aset.c (r1.76 -> r1.77)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mmgr/aset.c?r1=1.76&r2=1.77)
pgsql/src/include:
pg_config_manual.h (r1.30 -> r1.31)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config_manual.h?r1=1.30&r2=1.31)