unreviewed documentation patch for invoke.texi

[Janis Johnson]

A documentation patch that I submitted on July 16 is unreviewed.  It
clarifies descriptions of -fprofile-arcs, -ftest-coverage, and
-fbranch-probabilities in invoke.texi:

  http://gcc.gnu.org/ml/gcc-patches/2001-07/msg01097.html

I'm copying this to Andreas and Jan because they have been working
in this area and can verify whether the changes are correct.

Janis