Optimize some comparison functions for EQ cases.

Add (or (eq x y) ...) to bit-vector-=, two-arg-char-equal, pathname=.
Document extensible sequence protocol

Based on patch by Jan Moringen from lp#994528
Add a transform for EQUALP.

Similar to the EQUAL one.

Also fix a bug in the EQUAL transform when types which include
specialized arrays inside them were resulting in EQUAL being
incorrectly folded to NIL.
Add defknowns for TWO-ARG-CHAR-* functions.

This avoids the checks for multiple values.