Language packs downgrade

[GoogleCodeExporter]

If a user downgrades the TSVN version, downgrading the language packs doesn't 
work. The language pack installer detects that there's already a newer version 
of the resource dll on the system and does not overwrite that newer version 
with an older version.

We have to allow such downgrades as well, since we allow downgrading TSVN.

Also, the language pack installer for 32-bit must refuse to install on an x64 
OS since the TSVN installer does the same.

Original issue reported on code.google.com by tortoisesvn on 23 Jun 2012 at 8:44