Merge branch 'stable'
shifting dependency on lib/jgit to version 3.3.0.201403021825-r.mvn.

this also includes shifting the url schema to the new central repository, and as the version name indicates, we are now pointing at a version imported from the maven artifacts (meaning filenames have slightly changed, and we're also dragging down source and docs bundles).
create test fixture package and start moving relevant code to it.

the reliance on MdmReleaseInitCmd to set up other tests is a little uncomfortable but also more or less inevitable.

i'm very unhappy about the visibility bump some random fields got in this change... it's embarassing how much of this project is still reeling from the pass-maps-everywhere python design port.  this should go away when we get to proper builder interfaces for command config.
move tmpdir logic to WithCmd to be more reusable.  TestCaseUsingRepository is now purely a wee wrapper around WithCwd.
add property for toggling whether to keep the test temp files, useful for debugging.
don't delete by default when a WithCwd is closed; it's fine for tests do inspections after leaving a cwd.  but of course, when a whole test method is done, clearing is a reasonable default.
create a fixture for a simple project repo.
create a helper method for listing files in a repo at a ref; seems like it's going to come up a lot in crafting tests.
add a sanity check to the projectAlpha fixture setup.

note that nested classes declaring tests are not run by the ant 'run-test' target.  since this is more for a sanity check against outright wrong programming than a useful regression test, that's acceptable.
convert all throws clauses in FixtureUtil methods for setup into fatal errors.  I'm not interesting in propagating signatures of unreasonable failures of setup code throughout tests.
actually, make a unique error type to indicate that a failure is something drastic in fixture setup (as opposed to something other parts of the system failed to handle)
apply the SystemReaderFilteringProxy hack/fix in our test case superclass (that "Invalid value: diff.algorithm=patience" thing where the contents of my homedir break jgit (sigh) is getting on my nerves again).
automatically prepare dirs as necessary when using WithCwd.
grammar fix in error message.
using the standard test superclass in ProjectAlpha.SanityCheck doesn't have to do its own tmpdiring.
create fixture for a simple release repo.

as with the introduction project repo fixture, some random fields in a command got a visibility bump, and this is ishy but should go away when we get to proper builder interfaces for command config.
remove tons of setup logic from TestMdmAddCommand and use the new fixtures system.  most of the SLOC in this test is now actually about the test; much improved.
typo fix
prefer throwing to returning MdmExitMessage when it's an nonsuccess
add test for MdmAddCommand failing on a version that doesn't exist