uname: normalize release and version

Most systems provide the full version number in the
'release' field and the kernel version in 'version'.
Minix used to split the full version number between
release and version which caused problems for pkgsrc
and other applications. This patch brings Minix's
uname in line with other systems such as NetBSD.
It also brings the getty banner in line with NetBSD.

Old Minix uname:
	sysname->Minix
	nodename->10.0.2.15
	release->3
	version->2.1
	machine->i686

New Minix uname:
	sysname->Minix
	nodename->10.0.2.15
	release->3.2.1
	version->Minix 3.2.1 (GENERIC)
	machine->i686

Change-Id: I966633dfdcf2f9485966bb0d0d042afc45bbeb7d
Importing usr.bin/uname

Changes to uname.c based on a patch by Antoine Leca.

Change-Id: I4c316221e288edd839e26a2af4cb59f28bf722c1