Find cmder files when running as Administrator.

When starting a shell as Administrator, the CMDER_ROOT variable is
not propagated from the parent (non-Admin) environment.
Fix this by using paths relative to %ConEmuDir%.

Fixes issue #94.
changing this line to:

    for /f "delims=?" %%i in ("%ConEmuDir%\..\..") do @set CMDER_ROOT=%%~fi

makes this work when cmder is installed to a path with spaces.