Fix compile error by including sstream
Remove old gyp file.

Refs https://github.com/mapnik/node-mapnik/issues/150
It's 7051a3e23b827868b2a9fb83f97d6360748d1a89 applied to the v0.7.x branch
Merge pull request #205 from gravitystorm/compile-fix2

Apply 7051a3e23 to v0.7.x branch