bug#2350: 23.0.90; compilation-mode inserts output in the wrong location

[Richard M Stallman]

    This is a fundamental problem in `narrow': its meaning is ambiguous.
    Sometimes it is used to pretend that the buffer is really smaller than
    it is, and other times it's used just to "focus" on a subpart.
    The implementation (i.e. most of the C and Elisp code) tend to take the
    first point of view, but sometimes users intend the other.

While that is true, as a general statement, it is clear what we should
do to fix this problem: Compilation mode should widen temporarily and
insert at the end of the whole buffer.

Rather than using save-restriction, it should preserve point-max
as a count from the beginning (the value of (point-max) itself).