Made a pass over the mtp directory:

	* GNUmakerules: Add a "check" target that runs the executables
	listed in the "TESTS" variable.

	* robots/GNUmakefile.in: Add "mtp" to the list of SUBDIRS.

	* robots/mtp/GNUmakefile.in: Testbed-friendly makefile.

	* robots/mtp/mtp.h, robots/mtp.c: Tweaks and bug fixes.

	* robots/mtp/mtp_test.c: Test case for mtp stuff.