coda breakage

	a) switch by loff_t == __cmpdi2 use.  Replaced with a couple
of obvious ifs; update of ->f_pos in the first one makes sure that we
do the right thing in all cases.
	b) block_signals() and unblock_signals() are globals on UML.
Renamed coda ones; in principle UML probably ought to do rename as
well, but that's another story.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>