remove: conf.config_file_age and repo.repo_config_age.

Don't play the config-file-age charade, the values are not used.
doc: api: Base.read_all_repos()
fixed JSON decode error in persistor.py (RhBug:1032455)
rename: Base.update*() -> Base.upgrade*()

To have the API sync with the preferred nomenclature.
doc: api: document marking packages for transactions in Base.
doc:  clarify 'Specifying Transaction' a bit.
refactor: Raise/catch proper exceptions in/by package-marking methods.
remove: Do not give package-marking exceptions translated messages.
refactor: Do not give package-marking exceptions long messages.
tests: Make tests independent of locale settings.
Support iteration over packages installed by the user.
Support printing of package names.
Add "history userinstalled" command (RhBug:884615)
tests: cosmetic: order packages in .repo files by name.
cli: fix grammar of some sentences.
po.localPkg(): return the right localpath. (RhBug:1034607)
remove: Package.localpath.

It's just a testing hack.
test_localPkg: test also remote packages
Set "history" reason to packages installed during undos.
remove: bunch of old, unused Base() methods.