pgsql-server: Recognize plpgsql EXCEPTION condition names at function

Log Message:
-----------
Recognize plpgsql EXCEPTION condition names at function compile time
instead of runtime, for better detection of invalid condition names
(and maybe a little more speed, too).

Modified Files:
--------------
    pgsql-server/src/pl/plpgsql/src:
        gram.y (r1.60 -> r1.61)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/pl/plpgsql/src/gram.y.diff?r1=1.60&r2=1.61)
        pl_comp.c (r1.78 -> r1.79)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/pl/plpgsql/src/pl_comp.c.diff?r1=1.78&r2=1.79)
        pl_exec.c (r1.115 -> r1.116)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/pl/plpgsql/src/pl_exec.c.diff?r1=1.115&r2=1.116)
        plpgsql.h (r1.50 -> r1.51)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/pl/plpgsql/src/plpgsql.h.diff?r1=1.50&r2=1.51)