Enabled PETSc 3.5
Changed if-condition for PETSc version according to the suggestion by Nori
Replace BaseLib::number2str with std::to_string.

Also remove the header StringTools.h everywhere.
Add a previously missing sstream include in DateTools.cpp.
[GeoLib] Another version for GEOObjects::getGeoObjects().

The commit is a preparation to access GeoObject objects via the geometry
name and the object name (patch name).
Merge pull request #448 from TomFischer/GeoLibGetGeoObjectsByName

[GeoLib] Another version for GEOObjects::getGeoObjects().
Merge pull request #456 from endJunction/StdToString

Replace BaseLib::number2str with std::to_string.
Added one more condition for PETSc versions
Merge pull request #450 from wenqing/forPETSc35

Enabled PETSc 3.5