fixed ftools overlay algorithms
code cleaning and minor edits in other algorithms
added support for all gdal/ogr formats in all providers
added support for pre and post execution hooks
Merge branch 'master' of https://github.com/qgis/Quantum-GIS

Conflicts:
	python/plugins/sextante/algs/ftools/Difference.py
	python/plugins/sextante/algs/ftools/Intersection.py
	python/plugins/sextante/outputs/OutputTable.py