Add feature to dependencies task to write file paths to a file.

The dependencies task can be somewhat time consuming for a large project. It would be good if there was a way to write the properties and filesets out to a file. Then that file could be imported by the ant build.

This might also be used for caching the list of dependencies. For example, the dependencies task could write out this file the first run. On subsequent runs, if the build.xml file and/or the pom.xml files used for dependencies have not changed, then the filesets could just be loaded from the file.

The file could be called something like target/dependencies.xml and look like the following:

<project name="autogenerated-dependencies-list" default="load-dependencies">
  <property name="org.codehaus.plexus:plexus-utils:jar" value="/home/me/.m2/repository/org/codehaus/plexus/1.5/plexus-utils.jar"/>
  <fileset id="org.codehaus.plexus:plexus-utils:jar" file="/home/me/.m2/repository/org/codehaus/plexus/1.5/plexus-utils.jar"/>
  <fileset id="compile-dependencies">
    <fileset file="${org.codehaus.plexus:plexus-utils:jar}"/>
  </fileset>
</project>