Export directories dspace.cfg and build.xml out of sync

The directories for the item export are defined in dspace cfg as:

org.dspace.app.itemexport.work.dir = ${dspace.dir}/exports
org.dspace.app.itemexport.download.dir = ${dspace.dir}/exports/download

These properties are not used in the build.xml, instead the paths are redefined in:
<mkdir dir="${dspace.dir}/exports" />
<mkdir dir="${dspace.dir}/exports/download" />

Thus the created directories and the configured directories can get out of sync.

The patch uses org.dspace.app.itemexport.work.dir and org.dspace.app.itemexport.download.dir in the build.xml.