pgsql: Adjust configure script to print the bison and flex versions in

Log Message:
-----------
Adjust configure script to print the bison and flex versions in use.
Minor rearrangements to make a few tests in a more logical order.

Modified Files:
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pgsql/config:
programs.m4 (r1.20 -> r1.21)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/config/programs.m4.diff?r1=1.20&r2=1.21)
pgsql:
configure (r1.554 -> r1.555)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.diff?r1=1.554&r2=1.555)
configure.in (r1.521 -> r1.522)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.in.diff?r1=1.521&r2=1.522)