Validate IProduct.sourceforgeproject, and apply retrospective data fix

[Gavin Panella]

Changes to IProduct.sourceforgeproject are subject to minimal
validation, little enough that a lot of the data we have is invalid. A
lot of the time we see that sourceforgeproject is a full URL, and
sometimes it's not even ASCII.

In fact, SourceForge requires that project names conform to RFC 1035,
section 2.3.1. I believe that the definition of <label> in that
section is what we're looking for.

A basic validation method, valid_sourceforge_product_name, is being
added to canonical/launchpad/scripts/sfremoteproductfinder.py. This,
afaict, implements a reliable check for <label>. This function should
be changed into a validator and used to validate changes to
IProduct.sourceforgeproject.

Additionally, we should apply a retrospective data fix. See
SourceForgeRemoteProductFinder.extractSourceForgeProjectName() for an
approach.

[Björn Tillenius (bjornt)]

Fixed in devel r7882.