orgit-status-open: use magit-status-internal

instead of `magit-status', which no longer
supports the SWITCH-FUNCTION argument.
orgit-log-{store,open}: kludge to support version 2.1.0 of Magit

Version 2.1.0 of Magit supports logs for multiple revisions.  Orgit
does not do so yet.  When storing a link to a multi-rev log it now
discards all but the first rev, but at least it no longer blows up
when using this version of Magit.
orgit-rev-store: support version 2.1.0 of Magit

The mode `magit-commit-mode' has been renamed to `magit-revision-mode'.
For the time being support both names.