msvc on windows breaks with singleton declared but gcc needs default visibility to avoid double singleton registration across dlls when using -fvisiblity=hidden
update out of date cairo reference images - refs #1781
scons: reduce noisy, non-critical configure output
first pass on an html report to view failures
+ mapnik_datasource parameters : handle unicode objects - convert to internal UTF8 representation
+ utf8 to/from utf16 implementation
put implementatio into .cpp to avoid exposing <windows.h>

Conflicts:
	include/mapnik/utils.hpp
Revert "scons: use VariantDir to avoid 'Two environments with different actions' error when building both cpp_tests and with PLUGIN_LINKING=static"

This reverts commit 2393453765cc9c96de0c0c5bce98984b5ef09f32.
fix marker bbox calculation - closes #1849
iwyu
tests for 1849
add more expected test files
raise cairo visual test diff above 0
make visual test failure comparison work with relative image paths
* add support for unicode (utf16) paths on windows
ignore grids in html error output
line clipping drops points so filter osm data to ensure only lines are being used in test
Start moving visual test usage from osm to csv plugin
further convert visual tests to use csv plugin over osm
finish removal of osm plugin from visual tests