repo: log callback calls to librepo.

All the failure scenarios are hard to induce, let's have a strong debugging
option in-place until this code settles down.

Related: RhBug:1070598
downloads: fix counting past 100% on mirror failures (RhBug:1070598)
tests: test_cli_progress uses StringIO to check the output.

Gives us more readable unit tests.
api: add Repo.set_progress_bar() to the API.

Related: RhBug:1071323
api: expose RepoDict.get_matching() and RepoDict.all() (RhBug:1071323)

Renames get_multiple() to get_matching() and changes the KeyError handling to
be more similar to what the builtin dict.get().

Drops property on all(), dict.values() isn't a property either.
added transifex support to cmake (gettext-export, gettext-update)
generated and synchronized translations with transifex
fixed Japanese translatated message (RhBug:1071455)
drpm: properly report applydeltarpm errors. (RhBug:1071501)
cli: better format the download errors report.
doc: in the faq, warn users who might install rawhide packages on stable. (RhBug:1071677)
New version: 0.4.17
build: 0.4.17-1
there is no arch called arm64 it is aarch64

Signed-off-by: Dennis Gilmore <dennis@ausil.us>
add support for ppc64le

Signed-off-by: Dennis Gilmore <dennis@ausil.us>
added distro-sync explicit packages support
changed documentation of distro-sync command