Rename RewriteTreeFilter to TreeRevFilter and make it public

Rename RewriteTreeFilter to TreeRevFilter and make it public

The current behavior of passing a TreeFilter to RevWalk has limited
usefulness, since the RevFilter derived from the TreeFilter is always
ANDed together with any other RevFilters. It is also tied fairly
tightly to the parent rewriting mechanism.

Make TreeRevFilter a generic RevFilter that matches modified paths
against any TreeFilter. This allows for more complex logic like
(modified this path OR authored by this person).

Leave the rewrite flag logic in this class, since it's closely tied to
the parent comparison code, but hidden behind a protected constructor.

Change-Id: Ia72ef591a99415e6f340c5f64583a49c91f1b82f