Enforce value length

[domob1812]

Disallow values longer than 520 bytes in the RPC commands name_update and name_firstupdate, and unify it with the value check in the Qt. I've tested that this successfully prevents "stuck names" on test-net, but it would be good if someone independently confirms that 520 byte values are still ok while 521 bytes make the name stuck (and that the patch guards against this).

[muneeb-ali]

I use 519 bytes to be on the safe side. I can confirm that 521 causes problems. I don't remember testing 520, but I use 519 as the max and since I used that I've never had any issues for names getting "stuck" (we've registered thousands of names via http://onename.io)

[domob1812]

I tried 520 on test-net, too, see name_history of "value-520". But before we merge this patch, I'd be happy if someone else could test 520, too, in case I messed up the test (or at least look at "value-520" on test-net and confirm that I didn't get the length wrong).

[phelixbtc]

check (old version):

>>> for i,x in enumerate([519, 520, 521]):
        rpc.call("name_firstupdate", ["test_" + str(x), r[i][1], r[i][0], x*"x"])
>>> for i,x in enumerate([519, 520, 521]):
    print rpc.call("name_update", ["test_" + str(x), "x"])

6ff29f859e6140d95459d18c393be28f448e0fc6380f000d41cd311d9b733def
40594a2638ef431bb4bde55b9d0fe34a00e3b1d0e1f67c60ef2eee36be886ea6

Traceback (most recent call last):
  File "<pyshell#284>", line 2, in <module>
    print rpc.call("name_update", ["test_" + str(x), "x"])
RPCError: {u'id': 16, u'result': None, u'error': {u'message': u'Error: Transaction creation failed  ', u'code': -4}}
>>> 

[phelixbtc]

The new version works with 520 and blocks 521. ACK