TIFF I/O

+ use generic std::istream
+ add open from char const* and size factory method
scons: fix g++ detection logic on OS X
re-enable tiff from string tests - refs #1805 - closes #1831
fix tiff compile against older than tiff 4.x
Geometry/Feature parsers -truncate 'where' message in on_error handler (currently 16 chars max)
fix compile in master after 8d5b983cb6861b since master still uses phoenix v2
Merge branch 'master' of github.com:mapnik/mapnik into static-plugins
fixup handling of linkflags