GUACAMOLE-2139: Ensure properties like "revision" remain safe for downstream use.

This also removes the need to publish the parent POM as part of the
release for guacamole-common and guacamole-ext.

.gitignore

@@ -1,2 +1,3 @@
 *~
 target/
+.flattened-pom.xml

pom.xml

@@ -207,6 +207,36 @@
                 </executions>
             </plugin>
 
+            <!-- Bake-in properties like ${revision} so that downstream users of
+            libraries can freely use these properties for their own purposes.
+            This also removes the need to publish the guacamole-client parent
+            pom.xml to Maven Central. -->
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>flatten-maven-plugin</artifactId>
+                <version>1.7.3</version>
+                <configuration>
+                    <flattenMode>oss</flattenMode>
+                    <updatePomFile>true</updatePomFile>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>flatten</id>
+                        <phase>process-resources</phase>
+                        <goals>
+                            <goal>flatten</goal>
+                        </goals>
+                    </execution>
+                    <execution>
+                        <id>flatten.clean</id>
+                        <phase>clean</phase>
+                        <goals>
+                            <goal>clean</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
         </plugins>
 
         <pluginManagement>