Build: Set Java 7 build target for all jars;

embedders (esp. Android) targetting 1.6 must
set javac.version=1.6 in override.properties and set
both bootclasspath variables.

apps/i2ptunnel/java/build.xml

@@ -28,7 +28,7 @@
 
     <!-- only used if not set by a higher build.xml -->
     <property name="javac.compilerargs" value="" />
-    <property name="javac.version" value="1.6" />
+    <property name="javac.version" value="1.7" />
     <property name="require.gettext" value="true" />
 
     <target name="compile" depends="depend">