POD tweak
Add failing test for nonexistant key fetch on immutable hash

	modified:   t/04_immutable/immhash.t
document restricted hash behavior

	modified:   lib/List/Objects/WithUtils/Hash/Immutable.pm
	modified:   lib/List/Objects/WithUtils/Role/Hash/Immutable.pm
POD tweaks

	modified:   lib/List/Objects/WithUtils/Role/Hash/Immutable.pm
immhash; Drop Hash::Util in favor of tie (like immarray)

Hash::Util's lock_keys behavior is somewhat annoying, in that an exception is
thrown if one attempts to retrieve an unknown key.

	modified:   lib/List/Objects/WithUtils/Role/Hash/Immutable.pm
Merge branch 'immhash-nosuchkey'

* immhash-nosuchkey:
  immhash; Drop Hash::Util in favor of tie (like immarray)
  Add failing test for nonexistant key fetch on immutable hash

Conflicts:
	lib/List/Objects/WithUtils/Role/Hash/Immutable.pm