Recent glibc versions introduced a futimens() function, that gzip
already implemented. So waiting for a proper usage of this function in
gzip, we rename the gzip internal function to gz_futimens().

Patch inspired by
http://lists.pld-linux.org/mailman/pipermail/pld-cvs-commit/Week-of-Mon-20070514/155476.html



Fixes bug #537

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>