This changes `elevate.cmd` to first try to execute the requested command *without* elevation. If the command failed (i.e., `ERRORLEVEL` was non-zero), then retry the command with elevation.
Fixes#510
%PATH% expands to the system plus the user variables,
so if user defined user-environment PATH, 'setx /M PATH "%PATH%;..."'
mixes user-environment PATH and system-environment PATH.