Move share impl into files ActionHandler.

Don't include partial files when sharing.
Add test coverage.

Filter documents as list is loaded for sharing, eliminating need to copy.
Rename MimePredicate to MimeTypes and drop the Predicate impl (since nobody was using it).
    Move additional mime type functioanlity to the class.

Input DocumentsAdapter.Environment and LoaderCallbacks in inner classes.
    This reduces the number of public methods hanging off of DirectoryFragment.
In DirFragment normalize access to context/activity and State.

Added an IntentAssert class with some handy assert methods.

Addressed xutan@'s comment from last CL.

Add friendly support for selecting documents in TestEnv.

Change-Id: I55ea78ab5bef3a2b2644f6e0a3384adeaba78599