magit-last-point: add prefix, make permanent buffer-local
cleanup magit-revert-buffer and magit-update-vc-modeline
magit-refresh-wrapper: fix refreshing status buffer

Only attempt to update the status buffer if it actually exists.
Update the status buffer even if there are no other buffers that
need to be updated.
magit-run*: only advertise key for *magit-process* if there is one
magit-need-refresh: ignore non-magit buffers

Do not add buffers to `magit-refresh-needing-buffers' that do not
actually need to be updated because their modes don't derive from
`magit-mode'.  This does not affect how file visiting buffers
are *reverted*, which is different from being "refreshed" (but is
also triggered in `magit-refresh-wrapper').
magit-refresh-wrapper: always revert file-visiting buffers

Previously this wasn't done when there were no magit buffers
that needed to be refreshed.
fix magit-item-highlight for default theme

In the default theme both `highlight' (which `magit-item-highlight' used
to inherit from) and the various `magit-diff-*' faces set the background
color.  Making the former override the latter, which then have no effect
whatsoever.

Since our faces have to make sense when using the default theme we have
no choice but to use some other face attribute for `magit-item-highlight',
even though there is a good change that this will break some third-party
themes.

So in case people start complaining, please tell them to contact the
maintainer of their themes instead and point them to this commit.

This finally fixes issue #133.
magit-revert-buffers: perform cheap tests first
magit-key-mode: don't delete other windows to show menu

Conflicts:
	magit-key-mode.el
magit-key-mode-command: kill key-mode buffer before calling command
magit-key-mode-command: cleanup
magit-key-mode-add-option: inverse test
sanitize tests/run-tests.el

* don't use defvar when let is enough
* use built-in functions to create paths
* add /path/to/magit/../DEPENDENCY to load-path
* test whether dirs exist before adding to load-path
tests/run-tests.el: /path/to/magit/../DEPENDENCY to load-path