fix error when sending thumbnail to master

The fracture object was always created on layer 1 only (when this layer is not visible, ops.object.editmode_toggle hence failed). Now creating the fracture objects on current active layer(s).

from Filiciss Muhgue (filiciss)

Fix for #26867

Hunted down and debugged with great help from Geoff Murphy

In convert_lens() changed 'try' test to 'hasattr' test (Campbell Barton's suggestion, thank you), added '_' between prefix and ob_name to get more readable layers' names in AE, plus minor spelling corrections.

modified def convert_lens to behave correctly when camera sensor fit is set to vertical.\nPrevious version worked accurately only when 'AUTO' or 'HORIZONTAL' sensor fit was used.\nPreserved compatibility with 2.60a not supporting camera sensor size.

- Removing our hardcoded redraw of the render panel due to issues with Cycles and modified render panels. If anyone knows how to append a button into an existing panel, do tell me. Alternatively, adding a panel to the top of a properties page.

- Fixed a bug with the cancel button never triggering due to checking the wrong list of sessions

by Mariusz Maximus & Jong89

(yes sir, it is a bugfix :P ).

- no need to use self.properties
- close the file (py3.3 reports resource leak)
- dont use camel case for property names
- use property definition formatting like other scripts in trunk.

involve any drivers.

* Scan for master failed and gave an script error. 

Beware: in mocap/__init__.py there was a very long bl_label (> 100 chars), which was troncated in UI (at least, _update_msg.py produced a troncated msgid for it). That should be avoided, imho!