tt761_keys_revamp branch is ready

[Vasily Chekalkin]

Hello.

Branch tt761_keys_revamp is ready to be landed back to trunk.

Changes (with numbers from ticket)

  1. Use keys only for paths.
  2. Made Iterator pure interface class.
  3. Implement HashIterator and ArrayIterator.
  5. Remove all code left in Keys for support iterators.

Item 5 is partially implemented.

I also add support to use non-string keys and non-pmc values in PMC 
Hash. Just because Hash.set_pointer is way too dangerous.

There is still 2 test failures in t/compilers/pct related to hash keys 
order. I'll be very appreciated if someone can give me idea how to fix them.

I also smoked Rakudo's spectest against branch. Rakudo occasionally 
failed with message "Method 'succ' not found". But this is leftover from 
GC cleanups.

My system is Debian/Lenny/i386 so smoking branch on different OS/CPUs 
will be very helpful.

-- 
Bacek.