treat package reason 'unknown' in push_userinstalled() as 'user' (RhBug:1049025)

Rather serious bug.
repos: disable fastestmirror by default. (RhBug:1051554)

Also make it configurable.
doc: groom the bandwidth, throttle option a bit.
New version: 0.4.12
build: 0.4.12-1
fix typo in the 0.4.12 release notes.
progress display: end(size=None) should never fail
report mirror failures.

Related: RhBug:1051554
test_drpm: Add some tests before calling base.download_packages()
drpm: add config options + docs, load updateinfo.xml
drpm: download delta packages if possible
get_package_target(): support the "donecb" callback
drpm: spawn delta rebuild jobs, report failures
drpm: display delta rebuilds as they finish
drpm: fall back to rpm download on drpm errors