Allow to install files with "horde" role. Tried fixing downloading

Allow to install files with "horde" role. Tried fixing downloading
external dependencies from unknown channels.

PEAR is apparently not meant to bootstrap itself. The workarounds
necessary to allow creating a new Config that takes the "horde" role
into account are awkward because a nicely place "static" when
initializing the PEAR_Config.

Automatically fetching new channels fails completely at the moment as
parsing a package.xml with unkown channels does not work. Need to find
a decent solution at a later timepoint.