ENH: add a new library path ordering algorithm to make sure -L paths will pick the correct libraries if possible

ENH: Changed over to using C++ for building flex/bison generated files.  It reduces the number of changes that need to be made after generation.

ENH: Split dependency scanning and checking into separate cmDepends superclass with language-specific subclasses such as cmDependsC.

ENH: Re-implemented cmGeneratedFileStream to look like a real stream and replace the destination file atomically.  This will avoid problems with the process being terminated while generating a file.