An equality assertion for ordered sequences (like lists and tuples).
For the purposes of this function, a valid ordered sequence type is one
which can be indexed, has a length, and has an equality operator.
Args:
seq1: The first sequence to compare.
seq2: The second sequence to compare.
seq_type: The expected datatype of the sequences, or None if no
datatype should be enforced.
msg: Optional message to use on failure instead of a list of
differences.