Fixed printing of objects with uninitialized name.
Fixed signature check for signatures of unequal length.
Added 'qualifiers' slot and <standard-method-combinator> class.
Replaced <linear-method-combinator> with <standard-method-combinator>.

There is no real need for two different combinators in the *core* language
specification, so the linear one goes away--standard combinator with only
primary methods used is equivalent to it.

Also I have refactored bootstrap binding between predefined and (future)
user-defined generics a bit. Now all shortcuts
    (if applied-to-predefined-metaobject?
        call-bootstrap-function
        call-regular-generic-function )
are wrapped into `safe:...` functions, just like `slot-ref` for example.
Merge branch 'standard-method-combinator'