Add control file in preparation for next release

Now that 1.6.8 is released, the next release should include
an extension SQL file allowing upgrade from 1.6.8.

Author: jcflack

pljava-packaging/build.xml

@@ -255,6 +255,10 @@ jos.close();
 			     simple update is possible, just repeat the next entry, with
 				 the from-version changed.
 			  -->
+			<utf8 dir="target/classes" includes="pljava--.sql"
+				fullpath=
+			"pljava/sharedir/pljava/pljava--1.6.8--${project.version}.sql"
+			/>
 			<utf8 dir="target/classes" includes="pljava--.sql"
 				fullpath=
 			"pljava/sharedir/pljava/pljava--1.6.7--${project.version}.sql"