pgsql: Provide for MSVC config equivalents of recently added configure

Log Message:
-----------
Provide for MSVC config equivalents of recently added configure options. Remove
any hardcoding of those options. Along the way, reorder the expression used to
calculate RELSEG_SIZE to make it slightly clearer. For now wal_segsize is only
allowed to have a value of 1 on Windows - we can relax that when we get full
large file support in the backend.

Modified Files:
--------------
    pgsql:
        configure (r1.593 -> r1.594)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/configure?r1=1.593&r2=1.594)
        configure.in (r1.559 -> r1.560)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/configure.in?r1=1.559&r2=1.560)
    pgsql/src/include:
        pg_config.h.win32 (r1.54 -> r1.55)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/pg_config.h.win32?r1=1.54&r2=1.55)
    pgsql/src/tools/msvc:
        Solution.pm (r1.40 -> r1.41)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Solution.pm?r1=1.40&r2=1.41)
        config.pl (r1.12 -> r1.13)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/config.pl?r1=1.12&r2=1.13)