pgsql: Fix RS_isRegis() to agree exactly with RS_compile()'s idea of

Log Message:
-----------
Fix RS_isRegis() to agree exactly with RS_compile()'s idea of what's a valid
regis. Correct the latter's oversight that a bracket-expression needs to be
terminated. Reduce the ereports to elogs, since they are now not expected to
ever be hit (thus addressing Alvaro's original complaint).
In passing, const-ify the string argument to RS_compile.

Modified Files:
--------------
pgsql/src/backend/tsearch:
regis.c (r1.3 -> r1.4)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tsearch/regis.c?r1=1.3&r2=1.4)
spell.c (r1.10 -> r1.11)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tsearch/spell.c?r1=1.10&r2=1.11)
pgsql/src/include/tsearch/dicts:
regis.h (r1.4 -> r1.5)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/tsearch/dicts/regis.h?r1=1.4&r2=1.5)