When making filename comparisons for recipes for priority calculations,
we need to split off any virtual prefix. Without this, BBCLASSEXTEND
version of recipes don't follow the priority settings they should.
[YOCTO #2933]
(Bitbake rev: 055b72a230e6b0b1cababd65372c62d9ddce385e)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>