Fixes missing worksheet layout when there is no PCB loaded and all random brightness changes for the Cairo rendering backend.

Pcbnew: fix a crash when a non ascii char (i.e. a char having a code > 127) is found in a text (see Bug #1246340).
Could be only a temporary fix (tested only with French non ascii chars).

Changed the used framebuffer object extension from ARB_framebuffer_object to EXT_framebuffer_object (compatibility reasons).

template<> -> template <>
Some more reformatting according to uncrustify results.

Added error messages for OpenGL framebuffer errors. This should eliminate quiet segfaults in case of drivers that cannot handle multiple attachment points for framebuffers.

Used in highlighting/routing code.

Added flipping mode.

Smarter way of the overlay rendering (overlay is always refreshed, while cached&noncached targets only if the viewport or items have changed).

Now it is more verbose and the status is checked at the right moment (previously it was fine with Linux, but on Windows it showed errors).