Buffer overrun when syntax fragment contains no terminating newline.

[John Darrington]

I've just pushed a change fixing some sporadic crashes in the gui.   

The bug (which took a bit of tracking down) turned out to be caused by
a buffer overrun in lexer.c (lex_source_get_).   In particular, we have
the code:

 const char *newline = rawmemchr (line, '\n');

But the documentation for rawmemchr says that it's unpredictable if
line does not contain a '\n'.

So this means our syntax parser can crash if we present it with a
fragment which is not newline terminated.   I wasn't aware that we
had such a limitation.     Does this need to be fixed, or at least
explicitly documented ?

J'