pgsql: Our interface code for Spencer's regexp package was checking for

Log Message:
-----------
Our interface code for Spencer's regexp package was checking for regexp
error conditions during regexp compile, but not during regexp execution;
any sort of "can't happen" errors would be treated as no-match instead
of being reported as they should be.  Noticed while trying to duplicate
a reported Tcl bug.

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        regexp.c (r1.54 -> r1.55)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/regexp.c.diff?r1=1.54&r2=1.55)