parsing options

[Clint Adams]

> -Pu, -PU upper_case
> 
> For the switches, a lower case letter enables the option (turns it on) and 
> an upper case letter disables it (turns it off).

> Note 2:  Option '-Pu' makes bogofilter case insensitive, which is the way 
> bogofilter has operated since day 1.  With "-Pu", words "test", "Test", and 
> "TEST" are all converted to "test".  All the recent tests of case folding 
> (or not folding) indicate that doing changing upper case to lower case is 
> really, really bad.

Enabling "upper_case" makes it case-insensitive?  Seems much more
confusing than -Pf and -PF to me.