More GTK3 Waf build system adjustments

Install the src/gtkcompat.h header and install data/geany.css if necessary.
Add a  few more things to remember when making a release
Autotools: replace use of deprecated INCLUDES in favor to AM_CPPFLAGS
Remove unused variables
Don't find start of word when whole word matching should prevent it
Disable start of word checkbox when whole word checkbox is enabled