MAKE-CONDITION reports names of missing condition classes properly

MAKE-CONDITION used to rebind the variable containing the name of the
requested condition class to the condition classoid and thus NIL when
the classoid was not found.

Fixes lp#1199223.
Add meta-comment
Fix non-top-level defstruct.

Ensure constructors share the lexical environment of defstruct.
Slight improvement to UPDATE-SYMBOL-INFO