That helps weed out some issues faces with svn plus helped me figure out some
misuses.

Most of the commands have been implicitly depending on os.getcwd(). This change
makes it always consistent and clear when dependence on the current directory is
needed.

Remove default arguments to scm.SVN.GenerateDiff and a few other calls to be
sure the refactoring was done right.

R=dpranke@chromium.org
BUG=
TEST=make sure most commands aren't broke


Review URL: http://codereview.chromium.org/8771042

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@114262 0039d316-1c4b-4281-b951-d872f2087c98