The new execdir is two levels below the root directory, while
the old execdir 'bin' was only one level below. This commit
adapts the discovery of oguilib that uses relative paths
accordingly. We determine whether we have the extra level in the same
way in which the Makefile defines sharedir, i.e. whether the last
directory part is 'git-core'.
Inspired-by: Steffen Prohaska <prohaska@zib.de> Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>