Make nar: and scijava: plugin prefixes work

Otherwise, because they do not use one of the two blessed groupIds,
Maven fails to resolve them from their prefix unless the project POM
declares them itself in its <plugins> section.

See:
http://maven.apache.org/guides/introduction/introduction-to-plugin-prefix-mapping.html#Configuring_Maven_to_Search_for_Plugins

pom.xml

@@ -776,6 +776,18 @@ Projects wishing to use pom-scijava as a parent project need to override the &lt
 				<groupId>org.fusesource.mvnplugins</groupId>
 				<artifactId>maven-graph-plugin</artifactId>
 			</plugin>
+
+			<!-- Enable 'nar:' goals. -->
+			<plugin>
+				<groupId>com.github.maven-nar</groupId>
+				<artifactId>nar-maven-plugin</artifactId>
+			</plugin>
+
+			<!-- Enable 'scijava:' goals. -->
+			<plugin>
+				<groupId>org.scijava</groupId>
+				<artifactId>scijava-maven-plugin</artifactId>
+			</plugin>
 		</plugins>
 
 		<!-- We use wagon-webdav-jackrabbit 1.0 for deploys, since it is