bitbake: BBhandler/data: Fix __inherit_cache duplication

bitbake: BBhandler/data: Fix __inherit_cache duplication

The inherits cache contains duplicate entries, some with the full patch, some
just starting classes/xxx. This is a waste of parse time and potentially
error prone. This patch fixes various pieces of code so the absolute paths are
always preferred and work correctly. The inherits_class function did not work
with full paths so the patch fixes this.

(Bitbake rev: f3a71e509af196391ec126d079cf1bd178e62ad5)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>