File exclusion support (e.g., with rbt diff -X pattern or

rbt post -X pattern) now behaves identically (with some caveats).

Previously, the case of having a pattern matching against the root of

the repository was not well defined and was misinterpreted by all

SCMClients. Now all patterns beginning with a path separator (e.g.

-X /pattern on Linux and Mac OS, and -X \pattern on Windows) are

treated as being relative to the root of the repository checkoutl.

However, because CVS generates diffs relative to the current working

directory (without an easy way to determine the checkout root), all

patterns (even those beginning with a path separator) are treated as

relative to the current working directory.
The documentation for the -X flag has been updated to reflect these

changes.
Unit tests have been added for Bazaar, Git, Mercurial, and Subversion

for generating diffs correctly with this new syntax. A unit test has

also been added for Perforce that checks that paths are normalized

correctly.

Ran unit tests.
Manually tested that files were excluded correctly using CVS.
Manually verified that all cases in issue 3776 are resolved:

Running rbt diff -X PATTERN in a subdirectory checkout

   works as expected.
We no longer rely on the Working Copy Root Path field of

   svn info.
Running rbt diff --repository-url URL -X PATTERN R1:R2

   works as expected when ran outside of an SVN checkout.