win32: workaround startup error with MSYSTEM env
Dll loading logging by windbg and gflags /i Meld.exe +sls
showed that when MSYSTEM is defined then first directory where meld
searches some DLL's changes from lib subdirectory
to just meld dir itself. I didn't found the reason for it.
This workarounds the problem by adding the required directory to PATH
if meld is both frozen and is runed with MSYSTEM defined.
Problem description at #267 (closed)