Bumping elementtree version to 0.1.5 to match plugman and support namespaced xml elements
Fixes a bug where cordova prepare bombs on a config missing a content
element
  - Changes an undefined check to falsey to cover random null value
    returned from elementtree

  Tested By: David Kemp <drkemp@google.com> via Medic
[CB-4774] Display proper error if cordova prepare run not in project dir.

cordova prepare fails with a cryptic error message if run not from
cordova project dir:
  TypeError: Arguments to path.join must be strings
Fixed it to display the usual:
  Error: Current working directory is not a Cordova-based project.