Made show(1) the default lproc. `list' and `display' changed a bit.

Already in 1984, MTR stated, that lproc should be show. I agree with him
on this point, but I strongly disagree there: ``if lproc is "mhl", use
mhlproc for consistency''. I thus removed this part and even more around it.
The code became simpler but additional arguments to `list' and `display'
are not recognized anymore. That won't be much inconvenience.