Correct illegal external file references so the plugin will compile with more recent Opencpn version 3.3.1117

There are some other bugs corrected such as isnan etc.
After these corrections, the plugin compiles using MSVC++ however it will not run in debug mode.
It also compiles in release mode and when run, menus work properly and climatology gribs work fine and routings can be done with climatology, but grib files do not display and routing with grib files does not work. This bug needs fixing badly. Have looked for grib_pi version checking but do not find any.