Fix :Git! on Windows.

Closes #301, #302.
Unify escaping rules for :Gedit with :edit

In particular, this makes `:Gedit file\ with\ spaces` work, and updates
the tab complete to match.

Closes #305.
Work around archaic encodings

Closes #304.
Revert "Fix handling of spaces in filenames."

This reverts commit 2fdf760cef0fa4bf66a0716f3f9e3366e9113f6d.
Revert "Revert "Support WIDE COLON in :Gstatus in some locales""

This reverts commit 7234b3eeed1be32899d8be6c27d3822c4fd78565.
Merge remote-tracking branch 'origin/master' into bug-fixes