commands: add postincoming explicit brev argument (API) Before this patch, postincoming() initializes 'brev' with 'checkout', but this isn't useful to activate/deactivate bookmark after updating, because 'checkout' is not a string actually specified at command line, but an already node-nized byte sequence. This patch adds postincoming() explicit 'brev' argument, and makes 'pull()' pass appropriate value. This patch adds 'brev' argument instead of 'brev=None', because 'brev=None' isn't reasonable value if checkout is not None.