pgsql: Fix version_stamp.pl to allow 'alphaN' version stamps.

Log Message:
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Fix version_stamp.pl to allow 'alphaN' version stamps. Not sure how
Peter did that without fixing this ...

Modified Files:
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pgsql/src/tools:
version_stamp.pl (r1.3 -> r1.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/tools/version_stamp.pl?r1=1.3&r2=1.4)