Don’t force wrapping when focusing in a direction would work (+test)

Think of the following layout:

 -------------
 | tab |     |
 | con | win |
 |     |     |
 -------------

The tabbed container on the left has two children. Assume you have focused the
second/right child in the tabbed container. i3 used to focus the first/left
container of the tabbed container when using 'focus right' (it wrapped focus).

With this commit, the default behaviour is to instead focus the window on the
right of the screen.

The intention is to make focus switching more intuitive, especially with tabbed
containers supporting 'focus left'/'focus right' in tree. You should end up
using less 'focus parent' :).

You can force the old behaviour with 'force_focus_wrapping true' in your
config.

Code coverage is 62.5% with this commit.

src/cfgparse.l

@@ -122,6 +122,7 @@ normal                          { return TOK_NORMAL; }
 none                            { return TOK_NONE; }
 1pixel                          { return TOK_1PIXEL; }
 focus_follows_mouse             { return TOKFOCUSFOLLOWSMOUSE; }
+force_focus_wrapping            { return TOK_FORCE_FOCUS_WRAPPING; }
 workspace_bar                   { return TOKWORKSPACEBAR; }
 popup_during_fullscreen         { return TOK_POPUP_DURING_FULLSCREEN; }
 ignore                          { return TOK_IGNORE; }