doc: fix Package references that are ambiguous now.

Related: b68a697.
fixed local downgrade error
fixed wrong named variable
fixed py3 error thrown by search command
rename: yumbase (case insensitive) -> base.

There's been no YumBase class since b8f76da (Jan 2013).
refactor: move ReinstallCommand in its own module.
tests: move Term tests to better file.
Fix Term.MODE setting under Python 3 in case of incapable tty stdout.
fixed local reinstall error
removed _enc method that did nothing without specspo
sync with transifex