Ensures 3rd party jars on path prior to build; builds egg, not egg-info

The clamp command now does the following:

1. If required third party jars are not already on sys.path, makes it so, so they can be used for any necessary subsequent clamping.

2. Runs an egg install

In particular, this means it's now possible to use the clamp command as the install command for the package; simply do something like the following:

````python
import ez_setup
ez_setup.use_setuptools()

from setuptools import setup, find_packages
from clamp.commands import clamp_command

setup(
    name = "romper",
    version = "0.1",
    packages = find_packages(),
    install_requires = ["clamp>=0.4"],
    clamp = {
        "modules": ["romper.topology"],
    },
    cmdclass = { "install": clamp_command }
)
````

There are two steps. First, it's necessary to subclass the install command, much like this blog post: http://www.niteoweb.com/blog/setuptools-run-custom-code-during-install

But there's a little more work to be done. There's some convoluted logic in setuptools that determines whether an egg should be built, vs egg-info:
https://bitbucket.org/pypa/setuptools/src/64078530af019b31b3feae5cab73bf5c48ce4898/setuptools/command/install.py?at=default#cl-51
So to get the desired egg install, simply do `self.do_egg_install()`