Fix parsing and printing of octal character escapes.

The lexer correctly identifies octal character escape sequences as 1-3
octal digits. However, the later code that converts strings to and from
lists of Chars incorrectly interpreted sequences of valid octal digits
of _any length_ as a single escape sequence. Therefor, strings such as
this:

    "\00216\003172\007IN-ADDR\004ARPA"

were parsed and pretty-printed incorrectly.
Update Changelog (March 2013)
Improve printing of SUERefs and Ident
Update README/Language Extensions for 7.4
harness: default TMPDIR /tmp/ for attributes
TypeCheck: Return Left str instead of fail str (do not rely on MonadError instance of Either)
Bump version to 0.4.2.1