This should make it easier for newcomers to get WALA up and running
from sources. One no longer needs to manually find "dx.jar" using
instructions given at
<http://wala.sourceforge.net/wiki/index.php/UserGuide:Getting_Started#Building_the_code>
or
<https://groups.google.com/forum/#!msg/wala-sourceforge-net/cBYsfEvYVG0/Ua52dyQQU-YJ>.
Those instructions were already out-of-date, anyway.
Given that an official release of "dx.jar" is available in Maven, it
would be nice to have Maven itself manage that dependency.
Unfortunately, it seems that WALA in general does not use Maven for
dependency management. As far as I can tell, the Maven configuration
just calls out to Ant for doing builds, including having Ant download
other needed components. If WALA ever moved to using Maven more
fully, downloading "dx.jar" could easily come along with that.
Ant "build.xml" files don't have a standard DTD or XML Schema; the
contents are simply too flexible for that. But we can at least
give each a stub DOCTYPE declaration. That's enough to satisfy
Eclipse's XML validator, which otherwise complains that these files
lack grammar constraints.