[ODE] configure improvements

[Bram Stolk]

Hello,

I've fixed the Makefile.am files so that it is now possible
to have srcdir != builddir.

This enables you to do something like this:

sh autogen.sh
cd ../
mkdir build.single
cd build.single
../ode/configure --prefix=$HOME/ode.single ; make install
cd ../
mkdir build.double
cd build.double
../ode/configure --prefix=$HOME/ode.double --with-double-precision
make install

This way, you can have as many builddirs as you want, using
a single sourcetree. Even if you use just 1 buildtree, it
is still adviced to build in a separate dir.

There is still a problem with builddir!=srcdir, because
there is a hardcoded "../../drawstuff/textures" in the source,
that makes it impossible to run the test demos from the
builddir.


To really clean up the autoconf/automake interface, we could
opt for the approach used in the plib project:
seperate configure.in files for the lib, and the examples.

If we went this route, we could do it properly, using sutff
like:

CXXFLAGS = `ode-config --cflags`

'make install' creates a file $prefix/bin/ode-config which
should be used by applications using ode. It's much like
fltk-config mechanism.
Currently, this mechanism is unused in ode.
We should consider using it.

One last point: why is libode.so installed in bin, not in lib?

    Bram