Ignoring Aptana .buildpath file
Runner is redefining ABSPATH. Not sure why. Perhaps WP-cli assumes it is
the only library interacting with WP and it does all setup itself.

Added a defined check before setting ABSPATH.
In Runner, the after_wp_load method is kicking off the interactive
session.

I don't want to always be interactive, sometimes I want to use WP-CLI
like a library and call it from other PHP code.

Adding an $interactive switch to the method and defaulting value to true
so that it is backwards compatible.