Undocumented primitives

Hi,

I recently noticed a warning for my words DLSHIFT and DRSHIFT already
beeing defined in Gforth.  I had re-implemented both words in plain
forth, as they were not mentioned in the manual.

Now looking into "prim" from the Gforth sources, I can find even more
undocumented primitives that I may have accidentally re-implemented here
and there:

ror / rol / dror / drol / arshift / darshift / mux / select / inc# /
'cell/' / cell- / fourth / third

cheers,

David