+ fix writing to std::stringstream

* if seeking pass the end  - grow buffer (stringstream!)
* seekp beyond current buffer size doesn't set failbit (clang/libcxx)
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
Merge branch 'master' of https://github.com/mapnik/mapnik
xadd expected cairo outputs for lines-shield test (via ubuntu precise)