+ improve c++ style
+ formatting
add missing attribute collector for markers symbolizer path expression - closes #1952
avoid a few uneeded copies
rollback to copying bbox member of filter_in_box - previous change led to odd node-mapnik shapefile query failure
merge with master
add visual tests for group-by feature - refs #916
fix initialization of hue and sat in rgb2hsl + fix rounding in hsl2rgb to be stable on 32 bit systems (no change on 64 bit) - refs #1954
add test data as followup to 87a2787a407003f1328a4b0a38692d372a257c22 - refs #916
renable hsla filter as 'scale-hsla' - refs #1954
disable failing test of #1913 for now
webp encoding/decoding support - refs #1955
update changelog after #1955
Merge branch 'master' of github.com:mapnik/mapnik into future-rendering-api