Fix SubImage::zero() zeroing the parent image
Revert behaviour of zero() to use memset blindly.

This will allow it to be used on non-POD data, but historically it was used
on technically C++98 non-POD data which is really POD and is now POD in C++11.
Add in --disable-ggdb flag to work around LLVM bug
Possible fix for bad X11 tests on OSX 10.8
Merge branch 'master' into remove_subimage

Conflicts:
	cvd/image.h