More work on objectstore dependencies.

Be explicit about what in galaxy.util is being used, don't fail if galaxy.eggs is unavailable - assume the actual dependencies will be there (boto and rods) if not fail just a little later. If nothing else, this should fix some failing buildbot tests (nosetests records a failure if it cannot import a file and it cannot import the s3 or irods object store files because of these imports).
Use relative imports in objectstore code.

Goal is to enable the whole module to be placed in lwr.objectstore.
Make sqlalchemy dependency in object store optional unless create is used.
Update objectstore XML parsing to stdlib's ElementTree implementation.

Eliminates dependency on older elementtree egg.
Add test cases for some basic object store types.

Namely tests for disk, hierarchical, and distributed stores - as well parsing.
Add an LWR object store implementation.

This changeset implements an object store implementation that delegates to a concrete remote object store instance via an LWR server. Can utilize existing LWR security mechanisms and multiple transport options.

Updates the Galaxy LWR client through LWR changeset 2333f57.

This changeset contains no tests for this new implementation, but the LWR contains the same code along with an integration test that spins up a temp LWR to test against - this test case demonstrating the lwr object store client and server can be found here : https://bitbucket.org/jmchilton/lwr/src/default/test/lwr_objectstore_test.py.