Interface:

- added submenu "Scripts" in both View3D->Object and Mesh menus.
  Put them on top (it's better to follow some guideline, so users don't have to search for "Scripts" submenu in a different position in each menu), feel free to change.
- added button 'previous win' to SpaceScript, makes accessing buttons win, for example, much faster.  Maybe all spaces could have this button.

BPython:
- added Window.EditMode(), to check, enter and leave edit mode.  Scripts that change mesh data need this to leave edit mode before making changes to the active (G.obedit) mesh, of course.
- updated script bevel_center to use the above function and also popup an error msg if the active obj is not a mesh.
- doc updates, minor fixes.

Forgot to mention in my previous commit that I also updated the "-P" command-line option (for running script files) to be able to run already loaded Blender Texts, too.  So, if you have a script called 'Text' in foo.blend, you can run it with blender foo.blend -P Text .