- Reverse the meaning of the -m option: warnings about multiple /

- Reverse the meaning of the -m option: warnings about multiple /
  operators per line or statement are now on by default, and -m turns
  these warnings off.

- Change the way multiple / operators are reported; a regular
  recommendation is always emitted after the warning.

- Report ambiguous warnings (both int|long and float|complex used for
  the same operator).

- Update the doc string again to clarify all this and describe the
  possible messages more precisely.