[Dev-luatex] friday check in

[Taco Hoekwater]

Hi,

Nothing big this friday, because I've been kept busy doing other
stuff this (short) working week. I've committed changes that
amount to the following:

* when an error message was printed, the utf-8 in the pseudo-buffer
   was utf-8 encoded yet again, this is fixed.

* invalid utf-8 sequences are now mapped to unicode code point 0xFFFD
   ("REPLACEMENT CHARACTER"), and the help text is adjusted accordingly.

* The only ascii control sequences written to the terminal verbatim
   are TAB, LF and CR. All others are represented using ^^X notation.
   This change applies only to the terminal, the log file continues
   to recieve raw bytes.

Have a nice weekend! Taco