pool_test.go reformatting

- uniformed all messages with actual value first, expected second
- clarified error messages
- made comments more readable
- shortened most very long lines

No functional changes.
FYI, here's how to read the actual crazy hexadecimal:

52 = OP_2 (as in 2 of 3)
21 = 33 bytes for the next key (SEC compressed)
(33 bytes that start with 03 and end with 2b)
21 = 33 bytes for the next key (SEC compressed)
(33 bytes that start with 02 and end with e3)
21 = 33 bytes for the next key (SEC compressed)
(33 bytes that start with 02 and end with 32)
53 = OP_3 (as in 2 of 3)
ae = OP_CHECKMULTISIG