pgsql: Add support for XML build option to MSVC build scripts.

Log Message:
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Add support for XML build option to MSVC build scripts.
Magnus Hagander

Modified Files:
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pgsql/src/tools/msvc:
Solution.pm (r1.4 -> r1.5)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Solution.pm.diff?r1=1.4&r2=1.5)