hash multithreading and cross language issue

[Sam Ruby]

I note that the perlscalar code is careful about multithreading issues 
(example: "if we morph to a string, first clear str_val so that after 
changing the vtable a parallel reader doesn't get a gargabe pointer"), 
but reuses a static PMC* intret.

The current PerlHash PMC coerces keys to strings, so the following will 
print bar:

  my %hash;
  $hash{1} = 'foo';
  $hash{"1"} = 'bar';
  print $hash{1};
Whereas the nearest equivalent in Python will print foo:
  dict = {}
  dict[1] = 'foo'
  dict["1"] = 'bar'
  print dict[1]
For Python support, it would be ideal if there would be a hash method 
entry in the VTABLE for each object.

- Sam Ruby