Log Message:
Update PC6001VX to 2.31.0.

Upstream changes:

2.31.0 2017/08/19

* make file dialog and setting dialog fullscreen for low resolution devices
  when the ALWAYSFULLSCREEN flag is specified on build
* fix sound call method which was not thread safe
* rewrite documents with asciidoc
* (Windows) update build procedure
  make 64 bit version buildable
  recommend to use fixed MSYS2 version
  PATH setting no longer necessary
* (UNIX) fix pro file to build on non-Linux UNIX systems
* (non Windows) use absolute path for config files etc.
* (Android) temporary workaround for access issue of file access on a SD card