Class PluggableDictionary allows the redefinition of hashing and equality by clients. This is in particular useful if the clients know about specific properties of the objects stored in the dictionary. See the class comment of PluggableSet for an example.

Instance variables:
hashBlock <BlockContext> A one argument block used for hashing the elements.
equalBlock <BlockContext> A two argument block used for comparing the elements.

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	copy postCopyBlocks

	private
	scanFor:

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	equalBlock Return the block used for comparing the elements in the receiver.
	equalBlock: Set a new equality block. The block must accept two arguments and return true if the argumets are considered to be equal, false otherwise
	hashBlock Return the block used for hashing the elements in the receiver.
	hashBlock: Set a new hash block. The block must accept one argument and must return the hash value of the given argument.
	keys Answer a Set containing the receiver's keys.

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	copy Must copy the associations, or later store will effect both the original and the copy
	postCopyBlocks

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	scanFor: Scan the key array for the first slot containing either a nil (indicating an empty slot) or an element that matches anObject. Answer the index of that slot or zero if no slot is found. This method will be overridden in various subclasses that have different interpretations for matching elements.

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	integerDictionary