Removed chromedriver requirement from preflight 
script
Sets chromedriver based on its location on PATH

If the user doesn't have chromedriver, it just
neglects to set the property. We should probably
add a warning but only when/if the user instantiates
a ChromeDriver isntance.
Adds which and java to the dependencies.

Dependencies really out to be an object of names to versions for version
safety.
Blows up if chromedriver isn't on the PATH

And only blows up if and when the user tries to instantiate a 
ChromeDriver
Ignore .DS_Store (Mac OS X)
Re-add support for chromedriver in .webdriver-sync

Backwards compatibility for folks with chromedriver in ./.webdriver-sync
and without that on their path. PATH wins.
Off-topic: Allow ENV var to override selenium path

Didn't feel worth branching off this branch to do it, but now users
can specify their selenium path with an environment variable.
Downgrade the Selenium jar from error to warning

Since the jar isn't actually required at install-time, merely complain
if the jar file isn't found.
Update README to add awareness of ENV selenium jar
Throw runtime error if the Selenium jar is missing

Pulls out the message and the search for the selenium jar into a find()
method. Warns the user at install time and throws a runtime error at
runtime when the Jar can't be found (first at the ENV var and second
in the fixed static path)
merging from searls. sleep is failing.  need to checkout master to investigate