Correct dict_hash to our most recent version.

Correct dict_hash to our most recent version.

Several changes to dict_hash from Adacore's local version were inadvertantly
left out of the last change to that function.  These changes conservatively
cause dict_hash to revert to msymbol_hash_iw in more cases where the symbol
being hashed is known not to be Ada-encoded.  This avoids a few cases where
the function hashes large groups of names with similar prefixes to the same
value.

Changelog:

	gdb/
	* dictionary.c (dict_hash): Revert to msymbol_hash_iw in
	more cases.