Initial import of Baserock import tool for importing foreign packaging
Store dependency info in a separate file, not in the chunk morphology

This means that the tool can work without requiring changes to Morph to
allow new fields in morphologies. It also makes it easier to throw away
the foreign dependency information once an import is complete.

The downside is that there are now 3 types of extension, not two, and
a lot of code needed factoring out into base classes (and more needs
factoring out still). There are now .to_lorry, .to_chunk and .find_deps
extensions.
Improve README.rubygems
Update README slightly
Tidy up Ruby code

Use \ for multiline strings in Ruby instead of +.

Change 'raise Exception' to just 'raise', because Exception is the
default type.
Reorganise, tidy and document code of main application
Organise import extensions and data into subdirectories

Finally the repo starts to look a little more tidy!
rubygems.to_lorry: Remove trailing newline from exception message
Document and clarify code of main import loop
Add setup.py and move exts/ inside baserockimport package

It's slightly annoying during development, but the exts/ must be inside
the package or it would be installed somewhere silly like
/usr/lib/python2.7/site-packages/exts.
Some code has been merged with morphlib

This version of the import tool requires morph.git commit
6779e46e880eec757a6923441accef2442007677 or newer.
Remove .py from the program filename
Be more consistent that definitions-dir must be a Git repo

If we create the definitions-dir we also initialise it as a Git repo,
now.

I also deleted a no-longer-needed hack.
Make baserock-import binary executable
Fix some file locating and move data/ inside the baserockimport package

Now data/ actually gets installed too.
setup.py: Force import extensions to have execute permissions preserved

Code for this was taken from Morph's setup.py file.

It would possibly be more correct to install these files into a
subdirectory of /usr/libexec but it'd be a more complex solution for
little actual benefit.
Clean up use of a temporary file slightly
Don't force the generated stratum through morphloader validation

We should be able to trust it, since we literally just generated it.
omnibus: Simplify 'bundler exec' call

There's no need for quite so many subshells.
omnibus: Fix chaining to rubygems.to_chunk