= SET     var[=[value]]
     SET     < env-file

       - Same as EXPort cmd, set environment variable.
         Use to set, PATH etc, environment variable required for OS Native cmd.
       - On cmd-result-panel,to display all valiable enter cmd verb only.
         Following native cmd is executed.
         "env" for unix, "set" for else.
       - "set var":display current value. "set var=":reset
         "set < env-file": set by env-file.
         env-file record format:
            [set|export] var=[value] [comment]
       - ::xe.env(xe.env in workdir) is read at xe start if exist.
         ::xe___.env(___:OStype, ex.xewin.env) is read alternatively
         if exist.