pgsql: Turn most vc build scripts into modules instead of scripts, and

Log Message:
-----------
Turn most vc build scripts into modules instead of scripts, and just have
skeleton scripts calling them. To make it easier for the buildfarm
(or other "outside callers") to use these modules directly.

Per suggestion from Andrew Dunstan.

Modified Files:
--------------
    pgsql/src/tools/msvc:
        README (r1.4 -> r1.5)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/README.diff?r1=1.4&r2=1.5)
        Solution.pm (r1.15 -> r1.16)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Solution.pm.diff?r1=1.15&r2=1.16)
        install.pl (r1.5 -> r1.6)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/install.pl.diff?r1=1.5&r2=1.6)
        mkvcbuild.pl (r1.16 -> r1.17)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/mkvcbuild.pl.diff?r1=1.16&r2=1.17)
        vcregress.bat (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/vcregress.bat.diff?r1=1.1&r2=1.2)

Added Files:
-----------
    pgsql/src/tools/msvc:
        Genbki.pm (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Genbki.pm?rev=1.1&content-type=text/x-cvsweb-markup)
        Install.pm (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Install.pm?rev=1.1&content-type=text/x-cvsweb-markup)
        Mkvcbuild.pm (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Mkvcbuild.pm?rev=1.1&content-type=text/x-cvsweb-markup)