Don't execute menu commands if we're at a breakpoint

This pull request contains a horrible, horrible hack. I am ashamed to have written this code. There must be a better way to do this, but I haven't been able to find it. Please think twice (or more) before merging this request... 

Here is the scenario: you're hacking away on Brackets and need to hunt down a bug in the Brackets code. You open the Dev Tools, browse through the scripts, and set a breakpoint. Your breakpoint is hit. Life is good. While still at the breakpoint, you go back to Brackets and select a menu item (or press a menu shortcut). The command is executed. WTF? I thought I was at a breakpoint!?!? Well, guess what, you _were_ at a breakpoint, and the menu command was executed anyway. As you can imagine, this could lead to Very Bad Things.

On to the hack... I could not find a reliable way to determine if Brackets was being debugged, and at a breakpoint. The only possible solution I could think of is to look at the stack at the time `ShellAPI.executeCommand()` is called. Under normal circumstances, this is the _only_ call on the call stack. If you are at a breakpoint, I noticed that all of the code up to the breakpoint is _also_ included on the stack. Read the code to see the hack. 

Excuse me while I hide my head in shame.