moved minibatchsourcehelpers.h to Common/Include, as it is shared amongst readers (exception: the HTK reader, which has a different version);
fixed some incorrect #include of basetypes.h;
copying of DLLs now does not copy if the file already exists and is not out of date;
prebuild.bat now only updates builddate.h if it has changed, to avoid CNTK.cpp to be recompiled each time;
fixed a few build warnings in the CUDA kernels (uninitialized variables);
removed unused PTasks references in Linux makefiles
c380b98a54