GCC warnings on linux

[bmcage]

When compiling version on Ubuntu, 3 warnings are given. Ideally code can be adapted to avoid these warnings. Probably not a big issue however:

[ 80%] Building CXX object Core/CMakeFiles/TexGenCore.dir/SimulationAbaqus.o
/media/benny/hd2/datahd2/git/TexGen/Core/SimulationAbaqus.cpp: In member function ‘virtual std::vector& TexGen::CKeywordMaterial::GetConstants()’:
/media/benny/hd2/datahd2/git/TexGen/Core/SimulationAbaqus.cpp:1146:17: warning: reference to local variable ‘Constants’ returned [-Wreturn-local-addr]
vector Constants;

[ 83%] Building CXX object Core/CMakeFiles/TexGenCore.dir/TetgenMesh.o
/media/benny/hd2/datahd2/git/TexGen/Core/TetgenMesh.cpp: In member function ‘void TexGen::CTetgenMesh::SaveTetgenMesh(TexGen::CTextile&, std::__cxx11::string, std::__cxx11::string, bool)’:
/media/benny/hd2/datahd2/git/TexGen/Core/TetgenMesh.cpp:339:36: warning: ISO C++ forbids converting a string constant to ‘char*’ [-Wwrite-strings]
tetrahedralize("d", &m_in, &m_out);

[ 97%] Building C object Core/CMakeFiles/TexGenCore.dir/__/units/units.o
/media/benny/hd2/datahd2/git/TexGen/units/units.c: In function ‘reduceUnit’:
/media/benny/hd2/datahd2/git/TexGen/units/units.c:541:11: warning: implicit declaration of function ‘isspace’ [-Wimplicit-function-declaration]
while ( isspace(*unitString) ) unitString++;