Fix focus top left window bug

[wolever]

With newer versions of Vim, the top left window will be focused after
opening the fuf menu. This patch restores the window focus after the
menu is closed.

Nb: hasn't been tested on older versions of Vim.

[ernstki]

@wolever Thank you very much, kind traveler.

Not obvious from your PR description, but it also appears to fix the very annoying behavior of opening the result of, for example, a :FufBuffer selection in a split other than the current one (unless of course, the current split is topmost and left-most), a circumstance that had almost caused me to give up on FuzzyFinder forever.

Since it seems not very likely this will ever be merged in (unless FuzzyFinder gets a new maintainer), here's how to generate a patch file from this PR and apply it to an existing installation of FuzzyFinder.

# I use Pathogen, so your installation path might be different
cd ~/.vim/bundle/FuzzyFinder
curl -Lo fix-top-left-focus-bug.patch https://github.com/vim-scripts/FuzzyFinder/pull/2.diff
patch -p1 <fix-top-left-focus-bug.patch

[bemurphy]

@wolever you just saved me so much headache, this is amazing. Thank you!

[wolever]

Thank you again, @ernstki! I just moved to a new machine, had the same bug, and used your same solution :)

For any future folk who find this, here's the content of the diff, just in case something happens to it:

diff --git a/autoload/fuf.vim b/autoload/fuf.vim
index fe9e6eb..78be490 100644
--- a/autoload/fuf.vim
+++ b/autoload/fuf.vim
@@ -706,6 +706,11 @@ let s:FUF_BUF_NAME = '[fuf]'
 
 "
 function s:activateFufBuffer()
+  " Save the last window number so we can switch back to it later (otherwise,
+  " at least with more recent versions of Vim, we end up with the top left
+  " window focused)
+  let s:fuf_buffer_last_winnr = winnr()
+
   " lcd . : To avoid the strange behavior that unnamed buffer changes its cwd
   "         if 'autochdir' was set on.
   lcd .
@@ -733,6 +738,7 @@ function s:deactivateFufBuffer()
     AutoComplPopUnlock
   endif
   call l9#tempbuffer#close(s:FUF_BUF_NAME)
+  exec s:fuf_buffer_last_winnr . "wincmd w"
 endfunction
 
 " }}}1