When you have nested repos of different VCS and you edit a file from the inner
repo, more than one VCS can return a valid diff. Only one VCS should return a
non-empty diff, though.
Once a non-empty diff is found, all other VCS get disabled to reduce overhead.
References #235.
`:SyDebug` is displaying info if an alternate buffer is set. This
occurs because a buffer number of 0 represents the alternate buffer.
Using a 1-based range in sy#debug#list_active_buffers fixes this.
Signed-off-by: James McCoy <vega.james@gmail.com>
References #97.
