Avoid rounding errors comparing envelopes
Merge pull request #1948 from tomhughes/python

Avoid rounding errors comparing envelopes
Accept a few changes to visual test xml via harfbuzz branch - refs #1950
Add a few expected images
link mapnik first (needed static linking on linux)
shapeindex: if statically linking then bring in mapnik dep libs
scons: no need to link iconv if building with cairo
scons: only hardcode static linking libs on os x
scons: static linking on linux needs -dl for executables
scons: more linux static linking fixes
fix syntax
fix syntax
scons: link bindings to rt on linux
display png error when we cannot read a png
scons: link zlib last
+ improve c++ style
+ formatting
add missing attribute collector for markers symbolizer path expression - closes #1952