Added the ability to specify shell per pane.

Had to implement the special case for the first pane. In that case the
shell for the window that is created has to be overridden.

This also fixed a bug (in my opinion) that `window_shell` only affected
the first pane, and none of the other panes in a window.

The system unfortunatelly still bailes out, when the specified shell is
not executable (e.g. doesn't even exist). The problem is an unhandeled
exception when the information for the pane can't be extracted (as it
never really started). Not sure how to catch that and provide a sensible
message to the user.

Author: jerri

tmuxp/workspacebuilder.py

@@ -265,6 +265,13 @@ def iter_create_windows(self, session, append=False):
             else:
                 ws = None
 
+            # If the first pane specifies a shell, use that instead.
+            try:
+                if wconf['panes'][0]['shell'] != '':
+                    ws = wconf['panes'][0]['shell']
+            except (KeyError, IndexError):
+                pass
+
             w = session.new_window(
                 window_name=window_name,
                 start_directory=sd,
@@ -328,8 +335,20 @@ def get_pane_start_directory():
                     else:
                         return None
 
+                def get_pane_shell():
+
+                    if 'shell' in pconf:
+                        return pconf['shell']
+                    elif 'window_shell' in wconf:
+                        return wconf['window_shell']
+                    else:
+                        return None
+
                 p = w.split_window(
-                    attach=True, start_directory=get_pane_start_directory(), target=p.id
+                    attach=True,
+                    start_directory=get_pane_start_directory(),
+                    shell=get_pane_shell(),
+                    target=p.id
                 )
 
             assert isinstance(p, Pane)