cmds: add a way to launch actions in the background

Setting `guitool.<name>.background` will now launch custom commands in
the background, which avoids blocking the UI.

Related-to: #44

Suggested-by: Leho Kraav <leho@kraav.com>
Signed-off-by: David Aguilar <davvid@gmail.com>

cola/cmds.py

@@ -982,7 +982,10 @@ def do(self):
         Interaction.log(N_('Running command: %s') % title)
         cmd = ['sh', '-c', cmd]
 
-        if opts.get('noconsole'):
+        if opts.get('background'):
+            core.fork(cmd)
+            status, out, err = (0, '', '')
+        elif opts.get('noconsole'):
             status, out, err = core.run_command(cmd)
         else:
             status, out, err = Interaction.run_command(title, cmd)
@@ -991,7 +994,7 @@ def do(self):
                                out and (N_('Output: %s') % out) or '',
                                err and (N_('Errors: %s') % err) or '')
 
-        if not opts.get('norescan'):
+        if not opts.get('background') and not opts.get('norescan'):
             self.model.update_status()
         return status
 

share/doc/git-cola/git-cola.rst

@@ -489,6 +489,12 @@ receives the name of the tool as GIT_GUITOOL, the name of the currently
 selected file as FILENAME, and the name of the current branch as CUR_BRANCH
 (if the head is detached, CUR_BRANCH is empty).
 
+guitool.<name>.background
+-------------------------
+Run the command in the background (similar to editing and difftool actions).
+This avoids blocking the GUI.  Setting `background` to `true` implies
+`noconsole` and `norescan`.
+
 guitool.<name>.needsfile
 ------------------------
 Run the tool only if a diff is selected in the GUI. It guarantees that

share/doc/git-cola/relnotes.rst

@@ -50,6 +50,9 @@ Usability, bells and whistles
 
   https://github.com/git-cola/git-cola/issues/292
 
+* Custom `git config`-defined actions can now be run in the
+  background by setting `guitool.<name>.background` to `true`.
+
 Fixes
 -----
 * We now use bold fonts instead of SmallCaps to avoid