Merge pull request #902 from mispencer/CheckForMsbuildExe

Check for the existence of msbuild.exe as well.
Merge pull request #900 from mispencer/CygwinClientChanges

Call OmniSharpServer correctly in Cygwin
Cygwin should build compiled Python modules as dll
Windows cmake puts the dlls in RUNTIME_OUTPUT_DIRECTORY
Explicitly disable cygwin win32 legacy mode to avoid warnings