Adjust user thread queue size warning.
Remove incorrect execution of OP_0. That code was never reached, because OP_0 is not an opcode in terms of chunk.isOpCode()). However, it lead to believe that OP_0 pushes the vector [0], rather than correctly the empty vector to the stack.

Because the code was never executed, this bug could never trigger a test. Afaict, script.cpp does not have the corresponding case in its switch block.
Add script test to prove that OP_0 evaluates as the empty vector, rather than [0]. Also adds debug output in case an script_invalid.json test fails.
Merge branch 'schildbach/fix-script-OP_0'
Keep opcode in ScriptChunk representation of scripts. The goal is to know how data was pushed and be able to apply malleability rules. All unit-tests pass.
Include PUSHDATA opcode in Script.toString(). Also, smallNums are printed in their decoded form.