Merge pull request #28 from lpoujoulat/wxAuiExperimentalFixes

Fix for issue #6 and partial fix of issue #18: active pane management
-Small comment fix
- Introduced the wxEVT_AUI_PANE_CREATE_TAB
- Make wxAUI behave almost like current one regarding tab creation
- Allow to specify a terget pane in wxAuiManagerEvent
- Set the covered pane as the Target Pane in the wxEVT_AUI_PANE_CREATE_TAB event