rename "proto = detail" to "handler = detail"

rename "proto = detail" to "handler = detail"

"proto" is still accepted for compatibility.

However, it was too generic / conflicting, and was therefore
confusing.

Similarly, there were comments saying "listen load" would use
name2 to open the "load" module.  But name2 is now used for
something else, and the code was deleted a long time ago.