Don't call get_branch_name from assert_one_change

pyflakes reports:

git-review:464: local variable 'branch_name' is assigned to but never
used

Change-Id: I4b44feda65f2a5014107c7f606ada8550391b176
Changed the text of the manpage to read "make it easier to comprehend Gerrit".

Change-Id: If363cb4c5eeaa76f6d64bf0a1f431ff925f8ae2d
Merge "Don't call get_branch_name from assert_one_change"
Compare different Patch Sets of Review

Adds ability to fetch/checkout branches and launch git diff
for different review patchsets with one command.

Change-Id: I5815eb0cb6025978a39d74ddb31eb179f06154de