fix a few sign comparison warnings
fix possible crash in mapnik::process_layout::box_offset_align
fix #2239
shapeindex: more consistent error output
+ add eq/neq operators value_null <--> T
mapnik::value - return 'infinity' if rhs == 0 to avoid division by zero
do inherit dynamic library path
Merge branch 'master' of github.com:mapnik/mapnik
don't allow marker-spacing less than 1 - fixes #2218
Merge branch 'master' of github.com:mapnik/mapnik into flto
try clang 3.4