thumbor-9999.ebuild: Update to post v6.0

thumbor-9999.ebuild: Update to post v6.0

Bump from 97a5559 (5.2.0~3) to bc49cb3 (6.0.1-131-gbc49cb3).

Drop the Thumbor fork of pexif [1], the unused python-magic
dependency [2], gevent [3], pymongo [4], and pyvows [5,6] (but
not preggy [7]).

I have not included:

* The new argparse dependency [8] because Python 2.7 includes argparse
  [9].
* nose-focus, because the only current nose_focus use in in
  .coveragerc for a 'report' target, and we're only using the 'run'
  target.

Also bump from EAPI 5 to 6 and from git-2 to the newer git-r3 (there
were no changes impacting this ebuild [10]).

[1]: https://github.com/thumbor/thumbor/issues/294
     Subject: As pexif is now on pypi revert from thumbor fork
[2]: https://github.com/thumbor/thumbor/pull/734
     Subject: Remove unused python-magic dependency
     $ git describe --contains origin/pr/734
     6.0.2~10^2
[3]: https://github.com/thumbor/thumbor/pull/735
     Subject: Remove unused gevent dependency
     $ git describe --contains origin/pr/735
     6.0.2~11^2
[4]: https://github.com/thumbor/thumbor/commit/a733977c2d8da5fd6253535b8471c1afb3887a8a
     Subject: removing mongo from setup.py
     $ git describe --contains a733977c
     6.0.0b1~27
[5]: https://github.com/thumbor/thumbor/commit/f4c9e1fc7e77a4b8d5abc432e7afa60f77c816b2
     Subject: Setting tornado 4.1 version
     $ git describe --contains f4c9e1fc
     5.0.0-rc1~4
[6]: https://github.com/thumbor/thumbor/commit/1e985972b8c08d27b289bb306b075194cc960ee5
     Subject: Removed pyvows
     $ git describe --tags 1e985972
     6.0.1-91-g1e98597
[7]: https://github.com/thumbor/thumbor/pull/743
     Subject: Make dependency on preggy explicit
     $ git describe --contains origin/pr/743
     6.0.2~7^2
[8]: https://github.com/thumbor/thumbor/pull/588
     Subject: Feature/nosetests #
     $ git describe --contains origin/pr/588
     6.0.0b1~30^2
[9]: https://docs.python.org/2.7/library/argparse.html
[10]: https://devmanual.gentoo.org/ebuild-writing/eapi/#eapi=6