pgsql: Fix computation of PG_VERSION_NUM by configure: remove

Log Message:
-----------
Fix computation of PG_VERSION_NUM by configure: remove unnecessary and
unportable backslashes in awk script (per Patrick Welche), and add
brackets to prevent autoconf from mangling sed's regexp (the sed call
here never did what was expected).

Modified Files:
--------------
    pgsql:
        configure.in (r1.515 -> r1.516)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.in.diff?r1=1.515&r2=1.516)
        configure (r1.548 -> r1.549)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.diff?r1=1.548&r2=1.549)