Correct background region calculation for rotated view in dc-mode
Merge branch 'master' of https://github.com/OpenCPN/OpenCPN
render background chart correctly for raster charts in single chart mode with rotated viewports

this change corrects a7f724b4a62625cbc4cae5b6e254dd6bd2c39e17
I would like to see the coordinates used somehow reworked involving many more changes.
This would simplify the main render code in chcanv.cpp and glChartCanvas.cpp by changing
the calculations for each chart type.

For example, cm93.cpp:5254 really should not be testing for opengl
improve ui for texture cache handling, and support build without opengl
Merge branch 'master' of https://github.com/OpenCPN/OpenCPN
add fallthrough cases for plugin api 1.12
Merge branch 'master' of https://github.com/OpenCPN/OpenCPN
Correct quilt region calculation shortcut, again.
Simplify overzoom blur technique for POT textures.
Merge pull request #231 from seandepagnier/master

This appears to fix the issues with the background map in rotated dc-mode
Correct logic for recovery of lost keyboard focus on some PLugIn methods.
Peephole improvements in cm93 rendering performance.
Correct ChartBar flashing on Windows in OpenGL mode.
Correct cm93 initial viewport state.
Re-enable OpenGL Frame Buffer if not overzoomed
Improve PlugIn language support by forcing ocpn core to take precedence on translations.
Correct persistent chart quilting logic (FS#1628)
Update AIS target country name list. (FS#1626)
Correct Edition Date (ED) calculation for some BSB .KAP charts. (FS#1590)
Implement OpenGL FPS indicator on-screen.  Simplify overzoom blur for some simple systems.