Fix rbt status with Perforce.
Fix rbt status with Perforce.

rbt status broke with Perforce due to Perforce's assumption that
options.revision_range existed. We now do a conditional check like every
other SCMClient.

halvorlu/rbtools,datjwu/rbtools,beol/rbtools,davidt/rbtools,reviewboard/rbtools,reviewboard/rbtools,haosdent/rbtools,halvorlu/rbtools,beol/rbtools,datjwu/rbtools,davidt/rbtools,halvorlu/rbtools,datjwu/rbtools,davidt/rbtools,1tush/rbtools,haosdent/rbtools,haosdent/rbtools,beol/rbtools,reviewboard/rbtools