18.104.22.168: undefined warning and compilation unit summary tweaking
* Signal a full warning for undefined types when the name is in the
* Explain probable source of error when the name of an undefined type
is a quoted object.
* When same original source form is responsible for multiple
undefined warnings, only signal the first: otherwise we may signal
a boatload of identical warnings for a single source form just
because the compiler tries so very hard to make sense of it.
* Don't summarize the names of undefined things by signalling new
warnings for them, instead include the names in the compilation