Compilation fixes for linux (SCons build system)

- Unable to find ConvertUTF.h from CommonCharacterBuffer.cpp

- Missing _wfopen in CommonLogFileBufferFlusher.cpp, also
  missing include for fwrite, fclose, fopen, errno.
Merge pull request #2 from Nazg-Gul/blender-fixes

Compilation fixes for linux (SCons build system)