Comment 2 for bug 1070998

The error code doesn't say much:

Error 2 error C2338: The C++ Standard doesn't provide a hash for this type. (..\..\src\unit_tests\test_hashmaps.cpp) C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\xstddef 238 1 zorba_simplestore

but the error is on src\unit_tests\test_hashmaps.cpp:97:
std::unordered_map<zstring, int> map4(1024);

instead of zstring should be a primitive type.
std:string is allowed, but I think this will not fulfill the purpose of the test.