json/ext handles isolated escaped surrogates inconsistently

[mernen]

Using json 1.4.3, Ruby 1.8.7p174 and 1.9.2-preview1.

When given a high surrogate with no low surrogate, it gives nil for the string:

JSON.parse(%q{[123,"x\uD834x"]}    # => [123, nil]

When given a low surrogate with no high surrogate, it treats it as a valid character:

JSON.parse %q{[123,"x\uDD5Ex"]}    # => [123, "x\355\265\236x"]

In both cases, json/pure throws JSON::GeneratorErrors due to iconv's strictness (IllegalSequence on OS X, InvalidCharacter on Linux).

[hsbt]

Ruby 1.x is EOL at 2020.