pgsql: xcopy can only deal with forward-slashed paths when it's quoted -

Log Message:
-----------
xcopy can only deal with forward-slashed paths when it's quoted - needed
for "vcregress check" to work.
Per report from Dave Page.

Modified Files:
--------------
pgsql/src/tools/msvc:
Install.pm (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Install.pm.diff?r1=1.6&r2=1.7)