test_framework/script.py: Support for pretty-printing
test_framework/script.py: Support for pretty-printing

Use CScript.prettyprint(..) to create a better readable version
of a CScript. Example output:

OP_DUP OP_HASH160 8b139a5274cc85e2d36d4f97922a15ae5d7f68af OP_EQUAL
OP_IF
    OP_CHECKSIG
OP_ELSE
    OP_DUP OP_HASH160 f127e6b53e2005930718681d245fe5a2b22f2b9f OP_EQUAL
    OP_IF
        OP_OVER 4 OP_PICK OP_EQUAL OP_NOT OP_VERIFY
        OP_DUP OP_TOALTSTACK OP_CHECKDATASIGVERIFY
        OP_FROMALTSTACK OP_CHECKDATASIG
    OP_ELSE
        OP_RETURN
    OP_ENDIF
OP_ENDIF

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