pg-migrator - pg_migrator: Add code to check whether loadable libraries

Log Message:
-----------
Add code to check whether loadable libraries referenced in the old
installation are available in the new one.  The previous coding would
instead fail while trying to restore CREATE FUNCTION commands, which
is pretty annoying --- we want all common problems to fail in the
preflight check.

Modified Files:
--------------
    pg_migrator/src:
        info.c (r1.16 -> r1.17)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pg-migrator/pg_migrator/src/info.c?r1=1.16&r2=1.17)
        pg_migrator.c (r1.50 -> r1.51)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pg-migrator/pg_migrator/src/pg_migrator.c?r1=1.50&r2=1.51)
        pg_migrator.h (r1.59 -> r1.60)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pg-migrator/pg_migrator/src/pg_migrator.h?r1=1.59&r2=1.60)