octal escapes not tested

[smcv]

In JavaScript, "\012" or equivalently "\12" is a deprecated way to spell "\u000a" (same as "\012" or "\x0a" in C). In JSON, it's an undefined (hence invalid) escape sequence, just like "\x".

Different parsers might implement this differently (for example json-glib historically accepted "\012" as an extension) so it seems worthwhile to include in the test corpus.