Removed Exception_Abort because there is no windows version.  Also made ExitValue consistent with windows when a signal kills the process.

ENH: Added documentation to interface.  Finished process exit code interpretation implementation prototype.

BUG: Fixed check for existence of CMakeLists.txt file in top-level source directory before first configure.

ERR: Using GetCurrentProcessId instead of _getpid so we don't need to include the system process.h header.  Also creating pipe threads with 1K stacks to save memory.

ENH: EXECUTABLE_OUTPUT_PATH is now always set to get around cmake 1.6.7 dependency problems.  Moved default header directory inside the build tree instead of up one level.  User projects can now set the header directory.