Multiline messages can be passed to the reporting functions and exceptions.
Asserting and warning macros are adjusted accordingly. The locations where
they are used are similarly adjusted.

We no longer distinguish between reports which output only a single-line
message (argument M to macros) and such reports, which use output operators to
report additional values (argument V to macros). The string passed by M now
may contain newline characters as well as argument M may contain an expression
which makes use of stream output operators to print values of variables.