Like `read-char', but do not allow quitting.
Also, if the first character read is an octal digit,
we read any number of octal digits and return the
specified character code. Any nondigit terminates the sequence.
If the terminator is RET, it is discarded;
any other terminator is used itself as input.
The optional argument PROMPT specifies a string to use to prompt the user.
The variable `read-quoted-char-radix' controls which radix to use for numeric input.