Update the Visual Studio 2010 Projects

This updates the Visual Studio 2010 Projects in the following ways,
similar to the recent changes to the Visual Studio 2008 projects:

-Make all the copying of the pre-configured header files custom build
 rules, so that it is cleaner when people clean their builds, and the files
 can be re-copied when updated.
-Split up the property sheets, so to ease future maintenance
-Make the cogl-path library built as a DLL
-Build and link against SDL-2.x for SDL builds
-Make everything except the .sln file and the README.txt file use UNIX line
 endings, for easier maintenance.
-Merge cogl_sdl.sln and install-sdl.vcxproj into cogl.sln and
 install.vcxproj respectively.
-Update build of the conformance test to not use COGL_COMPILATION, and make
 it link to cogl-path.