commands: support passing depth to hg.clone()
This will allow extensions to add --depth or other arguments to control
depth fetching.
Differential Revision: https://phab.mercurial-scm.org/D5164
pager.pager=p0 # $TESTTMP/sysrc:4
ui.editor=e1 # $TESTTMP/userrc:2
pager.pager=p2 # $PAGER
ui.editor=e1 # $TESTTMP/userrc:2