Prevent buffer numbers from rapidly increasing.
Prevent buffer numbers from rapidly increasing.

Instead of creating two new temporary files every time a realtime diff is
performed, reuse the same two temporary files (per file extension).
This stops the plugin using hundreds of different temporary files.

Since the plugin now only uses a handful of temporary files we do not
need to wipeout the unlisted buffer created by vim for each index-blob's
temporary file.

In turn this means vim no longer needs hundreds of unlisted buffers, so
the next-available-buffer-number stays at sensible levels.

See #297.

airblade/vim-gitgutter