Fix: when using a search menu with an operator's enum prop, the operator was previously always executed with default options (appart from the search-set enum, of course). Now we store the op's properties in search button, so that you can specify non-default options (as it was already possible with e.g. pop-up menu from an operator's enum prop).

To achieve this, some code (callbacks and search button creation) was moved from wm_operators.c to interface/interface.c, and a new UI function was added, uiDefSearchButO_ptr.

Note: This new code uses the fact that uiButHandleFunc callbacks get executed before operator when one of its arg is the button itself!

Many thanks to Campbell who helped me a lot with this patch!

Cleanup: also removed two unused pointers from uiBut struct.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56063 954f8c5b-7b00-dc11-b283-0030488c597c