defer bounding box calculation, and use faster bounding box tests
consolidate and optimize clipping region logic
code formatting (whitespace change)
improve opengl extension function handling, and opengl setup
change GL_CLAMP to GL_CLAMP_TO_EDGE as the older setting is deprecated
grib plugin: add tooltip and improve warning message
Merge branch 'optimum-merging' into optimum

Conflicts:
	include/glChartCanvas.h
	include/s57chart.h
	src/NavObjectCollection.cpp
	src/Route.cpp
	src/chcanv.cpp
	src/glChartCanvas.cpp
	src/routemanagerdialog.cpp
	src/s57chart.cpp
use opengl texture for raster symbols if rectangle textures are supported
Merge branch 'optimum-merging' into optimum