use gendef instead of pexports when generating mingw import libs

pexports is no longer available for MinGW64
fixed building JNIs on Windows-64 with MinGW64

crosscompiling the Win32 JNIs on Win64 was tricky though,
I had to create an import library with:
i686-w64-mingw32-dlltool -k -A -p _imp_ --dllname ftd2xx.dll --def ftd2xx.def --output-lib libftd2xx.a
that would satisfy the references generated in JD2XX.o

also updated the precompiled Windows JNIs
added a ready-to-use JAR file

usually I'm against committing generated stuff but this simplifies
distribution of the binary