Homoclinic orbits in Bazykin's predator prey system

This example demonstrates how homoclinic orbits can be continued in HomCont
and how test functions can be used to detect certain codimension two
bifurcations of the orbits.

Note that we have added derivatives to the equation file baz.f
The files r.baz.n and s.baz.n correspond to the n-th run.

We start continuation from a periodic solution at alpha=0.427 and
delta=0.195, saved in the data file q.alpha.

0th run (of educational value): We continue the periodic solution in
PAR(1), PAR(2). The continuation stops with an MX error. Inspection of the
output shows that the homoclinic orbit breaks up near the equilibrium,
which indicates that PAR(11) needs to be increased. The reason for this is
that the unstable eigenvalue of the equilibrium is very close to 0 (almost
saddle-node eq.)
Note that ISTART=4 in s.baz.0 such that the periodic orbit is automatically
converted into an appropriate homoclinic orbit (automatic time-shift).

1st run: PAR(11) is increased to 4000.

2nd run: Continuation in parameter space and detection of saddle-node
bifurcation of equilibrium. Note that the test function (no. 10) needs to
be added to PSI and ICP.

3rd run: Continuation of detected saddle-node homoclinic orbit with
detection of non-central homoclinic orbit.

4th run: Continuation of homoclinic branch from the non-central homoclinic
orbit, found in the 3rd run at label 23. It is also checked for a resonant
(neutral) saddle.