pgsql: Make .pot files depend on the makefiles, so that they are updated

Log Message:
-----------
Make .pot files depend on the makefiles, so that they are updated when the
file or trigger function lists are changed.

Modified Files:
--------------
pgsql/src:
nls-global.mk (r1.18 -> r1.19)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/nls-global.mk?r1=1.18&r2=1.19)