'Core.v3-topa.76' message 'Handle byte-subclasses of byte-classes with _portableIsIndexable. Monticello-part is in Monticello.v3'

This was a blocker for #2 and #3, solves #4
'Monticello.v3-topa.458' message 'Allow for byte subclasses of byte classes ^M(have #byte type in Squeak/Pharo)'
Merge pull request #4 from krono/krono/issue-4

Sublcassing String creates non-loadable class ... ship it!