benchmark: png encoding with z=1 to ensure we're testing hextree not zlib
benchmark: break out string to int/bool/double conversions
make clean: also clear out shared libs
fix variable shadowing in placements_list.hpp
Various c++11 improvements
 - std::make_unique
 - avoiding uneccessary std::move calls which make actually prevent rvo (http://stackoverflow.com/questions/4986673/c11-rvalues-and-move-semantics-confusion)
 - more c++11 for loops
load_map: use const_iterator
stop testing bogus wkb since it will crash wkb reader - refs #2236
make css_value_broken truly broken with latest mapnik - refs #2237
simplify code