COMPRESS-199 XZ for Java doesn't provide an OSGi bundle, mark the dependency as optional

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1426283 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index 110e618..1fec7bc 100644
--- a/pom.xml
+++ b/pom.xml
@@ -151,6 +151,15 @@
           </archive>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.felix</groupId>
+        <artifactId>maven-bundle-plugin</artifactId>
+        <configuration>
+          <instructions>
+            <Import-Package>org.tukaani.xz;resolution:=optional</Import-Package>
+          </instructions>
+        </configuration>
+      </plugin>
     </plugins>
   </build>