New RNG

Here is the new RNG I talked about in the forums and I also replaced all rand() calls from gemrb core to use the new RNG:
```
rand % foo becomes RAND(0, foo-1)
rand & foo becomes RAND(0, foo)
```
I'd also like to replace the following rand() calls from the plugins:
```
./gemrb/plugins/CREImporter/CREImporter.cpp:                            stat=randcolors[i][rand()%RandRows];
./gemrb/plugins/CREImporter/CREImporter.cpp:                            stat=randcolors[i][rand()%RandRows];
./gemrb/plugins/FXOpcodes/FXOpcodes.cpp:                        fx->Parameter1 = rndstr->at(rand()%rndstr->size());
./gemrb/plugins/GUIScript/GUIScript.cpp:                                int i=rand()%5;
./gemrb/plugins/GUIScript/GUIScript.cpp:        if (rand()%100 >= percent) {
./gemrb/plugins/OpenALAudio/AmbientMgrAL.cpp:   int index = rand() % soundrefs.size();
./gemrb/plugins/PSTOpcodes/PSTOpcodes.cpp:                      ieWord tmp =(ieWord) rand();
```
but as soon as I do it, I get undefined references to the RNG class from the linker, though it is included in libgem_core.so after building. This is probably a CMake thing.