The Loader should seek towards the file system to find a collection

[mwildehahn]

This allows "invoke" to be called within sub directories of a project.

[bitprophet]

Note to self: #92 probably duplicates this.

[bitprophet]

#131 also semi related to this (though not exactly.)

In addition, I just pushed 625cb8e and e3ba34b which fix a commonish problem re: third party tasks.py modules masking "local" ones.

However, that's also only somewhat related - I'm not sure I understood what this ticket meant before but now I do, the scenario described is:

1. Have a folder with a tasks.py
2. Don't install it into Python's sys.path in any way
3. Enter a subdirectory
4. Try inv -l and watch it fail to find anything.

The reason I didn't really "get" this before is my typical scenario is to "skip" step 2 above - all my tasks.py are in Python projects installed to Python's path via pip install -e or python setup.py develop. When this is done, that tasks.py is now discoverable via sys.path and is then loaded by Invoke no matter where your CWD happens to be.

I'll try to actually review this PR (and compare it to #92) soon.

[bitprophet]

This should work as of the next feature release (or master :)). For more discussion see the latest comments on #92. Thanks!