clean_up: checking errno at exit does not make sense

It seems that at least FreeBSD is setting errno when malloc is
successful. There is a change that other operating systems will
do similar things with same, or other system calls, and this will
invalidate the idea of checking errno at exit.

See also email list thread for further information.

http://lists.freebsd.org/pipermail/freebsd-questions/2011-April/229150.html

Reported-by: Roar Pettersen <rope1968@gmail.com>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>