rename mmap() and munmap()

rename mmap() and munmap()

	. it's a good extra interface to have but doesn't
	  meet standardised functionality
	. applications (in pkgsrc) find it and expect
	  full functionality the minix mmap doesn't offter
	. on the whole probably better to hide these functions
	  (mmap and friends) until they are grown up; the base system
	  can use the new minix_* names