[gedit] Non-fast-forward update to branch wip/fix-external-tools

[Sébastien Wilmet <swilmet src gnome org>]

The branch 'wip/fix-external-tools' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  6ed9411... _gedit_tab_save_async() (wip)

Commits added to the branch:

  a59c15e... tab: save_async() and save_finish() to get the result