scons: fix the build in the case that one of the optional imaging libraries is not found
scons: ensure optional imaging libaries are build if requested when cross compiling
add webp to travis - refs #1955
scons: only compile optional cpp files that really can be built
remove RENDERING_STATS compile time option - refs #1956
pass string by const ref
tests: add a pseudo-tiled test for preventing regression of #1477
use featureset_buffer for simplier render time feature cache from @mappy
regression test for gdal filter-factor
remove filter_factor as option to gdal datasource, clean up pass down from query object - closes #1488 - refs #625
simplify render_style further after 6bbbe155fee3080aac0265b0f40805f2c2a4edde
clean up render_style code to avoid excessive function calls for marking a renderer as painted
Merge branch 'master' into skia-renderer

Conflicts:
	src/build.py
use freetype2 for calculating glyph's metrics (hack)
* use QGLWidget
* experimental GPU backend test (todo)