1bffffffffffffffff does not round-trip

[hildjj]

1bffffffffffffffff has to turn into a BigInteger in JavaScript when decoded. When re-encoded, that turns into c248ffffffffffffffff:

  c2                -- Tag #2
    48              -- Bytes, length: 8
      ffffffffffffffff -- ffffffffffffffff

If I special-case the encoding for BigIntegers that fit into 8 byte normal integers, then c248ffffffffffffffff won't round-trip. My suggestion is to just set roundtrip to false for this case.

[hildjj]

Other similar problems:

3bffffffffffffffff
f90000
f93c00
f97bff
fa47c35000
f9c400