Update Windows Builds Files to use ENV vars to find dependancies

Update the DevStudio project files to use ENV vars to locate the includes and libraries it needs

Proposed ENV vars

APR_DIST - Points to the location APR and APR-Util are installed in (e.g. C:\Program Files\APR)
CPPUNIT_DIST - Points to the CPPUnit install location
PLATFORM_SDK - Points to the versions of the platform SDK to use.