Add 'checkout' download command to patch sets

Alongside of pull we now offer 'checkout', which creates a detached
HEAD pointing at exactly the patch set chosen, rather than merging
with the current branch.

Change-Id: Ia34394f2c87fd77de4eab128563aa24238ab6961
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed