Implement FIND efficiently on vectors when start/end/from-end are supplied
Implement FIND efficiently on vectors when start/end/from-end are supplied

This was a major cause of slow-down in cl-jpeg, which is now 5x faster.
Additionally, this entirely eliminates consing along find's vector path.

varjagg/Mezzano,varjagg/Mezzano,rvedam/Mezzano,froggey/Mezzano,rvedam/Mezzano,froggey/Mezzano