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

lib/libc/syscall/mmap.S

@@ -1,6 +1,6 @@
 #include <machine/asm.h>
 
-IMPORT(_mmap)
-ENTRY(mmap)
-	jmp	_C_LABEL(_mmap)
+IMPORT(_minix_mmap)
+ENTRY(minix_mmap)
+	jmp	_C_LABEL(_minix_mmap)
 

lib/libc/syscall/munmap.S

@@ -1,10 +1,10 @@
 #include <machine/asm.h>
 
-IMPORT(_munmap)
-ENTRY(munmap)
-	jmp	_C_LABEL(_munmap)
+IMPORT(_minix_munmap)
+ENTRY(minix_munmap)
+	jmp	_C_LABEL(_minix_munmap)
 
-IMPORT(_munmap_text)
-ENTRY(munmap_text)
-	jmp	_C_LABEL(_munmap_text)
+IMPORT(_minix_munmap_text)
+ENTRY(minix_munmap_text)
+	jmp	_C_LABEL(_minix_munmap_text)