clone: avoid using repo.lookup() with binary nodeid The code in hg.clone() is a bit of a mess, but it seems like the "checkout" variable is always a binary nodeid (tests pass when run with "assert len(checkout) == 20" before the repo.lookup()). repo.lookup() will soon work only with string inputs, so we need remove this use. Differential Revision: https://phab.mercurial-scm.org/D3191