Adding `old-model` directory.

Adding files from `uniform` branch that implement the old msBayes model,
but with additional parameter output like the new implementation. The
goal is to avoid having to maintain a separate branch for the old model.
Renaming `msbayes.pl` to `dpp-msbayes.pl`.
Changing `msprior` executable name to `dpp-msprior`.

Updating `src/Makefile.am` to build `dpp-msprior` executable rather than
the old name `msprior`. Updating autotools auxiliary files accordingly
using: `aclocal; autoconf; automake`.

Also, updating `dpp-msbayes.pl` script to look for "dpp-msprior"
executable rather than "msprior".
Updating `Makefile.am` to install `dpp-msbaye.pl`.

Updating `Makefile.am` (and `Makefile.in` via `automake`). Changing name
of bin script `msbaye.pl` to `dpp-msbayes.pl`.
Updating autotools configuration.

Adding `--enable-old-model` option to configure to allow the old
implementation to be built and installed along side the new
implementation. This entailed modifying autotools auxiliary files and
updating the `include` statements of `src/old-model/msprior.h` and
`src/old-model/setup.c`.
Updating package name in `configure.ac`.

Changing package name from `msbayes` to `dpp-msbayes` and updating my
e-mail in `configure.ac`. Updating `configure` script accordingly via a
call to `autoconf`.