Add assorted aubio patches to get the current Git trunk working.

Add assorted aubio patches to get the current Git trunk working.

Also:
* Update to EAPI 4
* Update to `git-2` eclass
* Remove the `alsa` USE flag, since ASLA support was removed from
  aubio with:
    commit 705aec8b92b6bbe0394c6fe809706ad49828834e
    Author: Paul Brossier <piem@piem.org>
    Date:   Fri Sep 25 22:12:56 2009 +0200
      ext/midi: remove all midi stuff borrowed from fluidsynth, now unused
* Create an `m4` directory by hand to avoid:
    aclocal-1.11: couldn't open directory `m4': No such file or directory
* Break `econf` out into `src_configure` for EAPI >= 2.
* Don't try and install documentation that no longer exists.
* Other changes to catch up with the trunk's aubio-0.3.2-r2.ebuild.