Introduce alternative cmake based build system. Cmake is especially convenient
for building on Windows, as it can produce VC projects or nmake files and 
does not require cygwin to be installed. In addition on OSX Xcode projects
can be generated.


git-svn-id: http://root.cern.ch/svn/root/trunk@39463 27541ba8-7e3a-0410-8455-c3a389f83636