Fix missing RT_SCOPE_* defines on MinGW build
Added statvfs structure for MinGW build
Fixing libcore_io_Posix compilation under MinGW
Fixed some linking issues under MinGW
Fixed java_io_File.cpp under MinGW
Also some refactoring done of unicode defines (re-used from libcore_io_Posix.cpp)
Fixed java.io.File for Windows - now it replaces "/" with "\" upon creation (both separators are valid, but "\" is canonical for Windows, and file.separator is set to it)
Fixing build on non-Windows
Merge pull request #11 from bigfatbrowncat/upstream-merge

The new libcore is patched for Windows and OS X