Allow ALIASES and TREES to be merged in configs

Review Request #6649 — Created Nov. 26, 2014 and submitted — Latest diff uploaded

Information

RBTools
master
181965d...

Reviewers

Give special treatment to the ALIASES and TREES keys in
.reviewboardrc so that they are merged together and not overwritten.

Ran unit tests.

Created a ../.reviewboardrc and ./.reviewboardrc with different
aliases and was able to execute all of them.