bug#5677: help messages should be more forthcoming as to why they don't know where a function came from

[jidanni]

Sometimes we see
C-q runs the command quoted-insert, which is an interactive compiled
Lisp function in `simple.el'.

Sometimes we only see
tempo-template-html-header-6 is an interactive Lisp function.

I.e., where the function came from is a mystery.

I propose that the help functions involved say more as to why they can't
figure out where the function came from, and perhaps even invite the
user to report a bug if he knows where the function came from.