RRDtool and dotnet bindings under Win7 x64 with VS 2010

Hey,

I've just built from trunk (r2284) on a 64bit Windows 7 machine under VS 
2010, and made a few tweaks:

- explicit casts from void* to e.g. char* on malloc, realloc
- scoping to isolate variable init in switch cases
- stepped back to r2282 of rrd_graph_helper.c as I was hitting ERROR: No 
positional legend found on generating pngs in rrdtutorial
- wrangled the dotnet binding projects to x86 (fine for me for now)
- .def file doesn't seem to exist in rrdlib project -- I wrapped a copy 
of the public decls in rrd.h in a #ifdef WIN32 and added explicit 
__declspec(dllexport) to export the symbols

... just in case anyone's doing the same thing out there at the moment.

Cheers -- RRDtool still looks good :)