patchs to JNA wrapper functions
These patches are helpful for avoiding the compiler warnings pointed out by @claus.kleinwort in #2 (closed) . Besides patches to resolve those warnings, I also updated the CMakeLists.txt to help make the output cleaner (at least on my GCC machine). Labeling the external libraries as "SYSTEM" libraries allows the compiler to throw away any warnings generated by them since we are not currently interested in changing how those libraries are written.
Closes #2 (closed)