Importing usr.bin/nohup

Replaces commands/nohup. No Minix-specific changes needed.

Change-Id: I2fb7c387833a8898cf30fc3ac25ea53ee1031bd1
avoid alloc_contig() for iovec, mfs superblock

	. initial workaround for assert() firing on iovec
	  size on ARM. likely due to alloc_contig() allocating
	  unusually mapped memory in STATICINIT.
	. for the same reason use the regular cache i/o functions
	  to read the superblock in mfs - avoid the alloc_contig()
	  that STATICINIT does.

Change-Id: I3d8dc635b1cf2666e55b0393feae74cc25b8fed4