pylint #81078 Warn if names in exception handlers clobber overwrite existing names [open]

Exception handlers like the following are almost always wrong:

except KeyError, IOError:

In the current code, this creates (rather cryptic) error messages about
IOError being an invalid name for a local variable, and an inexperienced
programmer is more likely to silence it than to know the actual problem.

appeared in<not specified>
done in<not specified>
closed by<not specified>