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.

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.

ERR: Test for ansi streams may need to use iosfwd for test because some compilers provide an iostream header that is old streams.