Preprocessor: Rationalize, simplify, and correct the stack of input sources and their tokenization.  This included
 - consistently dealing with EOF and its effect on error recovery (bug 11444, #1)
 - turning a simulated OO hierarchy of function pointers and typecasting into a real C++ class hierarchy
 - correctly handling '\' everywhere, in all classes of tokens, as a layer before preprocessing itself
 - conditionally handling '\n' in macro expansion input, depending on whether it is in a macro expression or not
 - delete some unused "memory cleanup" code


git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@24626 e7fa87d3-cd2b-0410-9028-fcbf551c1848