coverage: byte-compiling elisp files in different subdirectories Where a '.el' file in a subdirectory might require a '.el' file in another one. This does not work out of the box, but can be made to work with a judicious use of $(AM_ELCFLAGS) (just introduced in the previous commit). * t/lisp-subdir-mix.sh: New test. * t/list-of-tests.mk: Add it. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>