Inconsistent hiding of the main menu top bar

The top bar can be hidden using the layoutExtraVars.vm file and the $displayMainMenu variable. However, this doesn't hide the top bar in edit mode.

To reproduce:

• Edit the layoutExtraVars.vm
• Change $displayMainMenu to false
• Open a wiki (the top bar should not be displayed)
• Edit any page (not in inline mode); the top bar is displayed when it shouldn't