Log Message:
Update onscripter to 20150820.

Upstream changes (no English changelog):

20150820:
 - change 'a' key (auto-mode) behavior as the original NScripter
   (affects only Android)

20150811:
 - make lsp and other insns accept decimal fraction as height and width
   values of rectangle drawing

20150810:
 - fix a bug in split insn that causes segfault when number of split
   characters is equal to or larger than 256 bytes
 - fix a bug of BGM loop on Android
 - fix a bug of gettag insn
 - fix a bug that LUA cannot recognize scripts which include '\'
   in the second byte of Shift-JIS chars
 - implement getmclick insn, and also implement NSGetClick, NSGetMouse,
   NSDoEvents, NSSleep, NSSpCell, NSSp2GetInfo, NSSp2GetPos, NSSp2Load,
   and NSSp2Move insns for NSLua
 - use the latest SDK and NDK for Android on Linux
 - speed up extracting zip files on Android