More robot-related tweaks and bug fixes:

	* robots/emc/emcd.c: Handle "-h" option properly.

	* robots/emc/loclistener.in: Pickup the pixels_per_meter value
	from the database and use that to convert event coordinates in
	meters to pixels for the database.

	* robots/primotion/gorobot.cc: Comment.

	* robots/primotion/dgrobot/gcallbacks.h,
	robots/primotion/dgrobot/gcallbacks.cc,
	robots/primotion/dgrobot/grobot.h,
	robots/primotion/dgrobot/grobot.c,
	robots/primotion/dgrobot/grobot_sim.cc: Small bug fixes to make
	sure the position estimate is updated when moving in a straight
	line.

	* robots/rmcd/rmcd.c: cleanup

	* robots/vmcd/GNUmakefile.in, robots/vmcd/test_emcd3.config,
	robots/vmcd/test_vmcd3.pos, robots/vmcd/test_vmcd3.sh,
	robots/vmcd/test_vmcd4.pos, robots/vmcd/test_vmcd4.sh: Some more
	test cases, still pretty simple though.