evl ps format output issues

Hi there,
when running evl ps -st there are some formatting issues that affect its machine-parseability:

- the STAT column often is empty (I know this could be obviated by using `-n`)
- if PID has 6 digits, then it will touch the ISW column and other columns also seem at risk of overflowing (very much a possibility for CTXSW, SYS and long running programs).

The above issues make it hard to use `/ +/` without manually fixing things up to split evl ps's output.

I suggest the following:
- reduce the width of all fields (not already starting with whitespace) by 1, prepending each with a space. This ensures that / +/ splitting works.
- change format_state() so that it always returns a non-empty string

If these changes seem reasonable, I'd be happy to provide a patch.

Best,
Giulio