Latest version of the patch attached with new warnings and info.
Example output...

$ sort --debug -rb -k2n +2 -1b /dev/null
sort: using `en_US.utf8' sorting rules
sort: obsolescent key formats used.  Consider using `-k'
sort: key 1 is numeric and spans multiple fields
sort: key 2 has zero width and will be ignored
sort: leading blanks are significant in key 2.  Consider also specifying `b'
sort: option `-b' is ignored
sort: option `-r' only applies to last-resort comparison

$ LANG=en_USA sort --debug -srb -k1,1n /dev/null
sort: using simple byte comparison
sort: options `-br' are ignored

I'll commit tonight sometime I think.

cheers,
Pádraig.