Nasal: fix parsing octal/hex numbers in strings as well as during lexing.

Nasal: fix parsing octal/hex numbers in strings as well as during lexing.

Parse the same number formats (octal, dec, hex) in literals and tokens. Was
previously quite a mess, and is still not the best solution, as lexing and
string parsing uses different implementations, although they are meant to
do exactly the same conversions.