Fix incompatible-pointer-type build error.

Make Xcode 5.0.1 happy by calling dictionaryWithObjectsAndKeys on
NSMutableDictionary instead of NSDictionary.

Fixes the error:
	Incompatible pointer types initializing 'NSMutableDictionary *'
	with an expression of type 'NSDictionary *'
Changing loop over buckets to keep going if one of the buckets encounters a decrypt error. Useful if not all buckets have the same password.