Support plantuml !include statement

Support the plantuml !include statement by using the newly defined PLANTUML_INCLUDE_PATH

src/config.xml

@@ -3302,6 +3302,14 @@ to be found in the default search path.
  java can find the \c plantuml.jar file. If left blank, it is assumed PlantUML is not used or 
  called during a preprocessing step. Doxygen will generate a warning when it encounters a 
  \ref cmdstartuml "\\startuml" command in this case and will not generate output for the diagram.
+]]>
+      </docs>
+    </option>
+    <option type='list' id='PLANTUML_INCLUDE_PATH' format='dir' defval='' depends='HAVE_DOT'>
+      <docs>
+<![CDATA[
+ When using plantuml, the specified paths are searched for files specified by the \c !include
+ statement in a plantuml block. 
 ]]>
       </docs>
     </option>

src/plantuml.cpp

@@ -56,7 +56,24 @@ void generatePlantUMLOutput(const char *baseName,const char *outDir,PlantUMLOutp
   static QCString plantumlJarPath = Config_getString("PLANTUML_JAR_PATH");
 
   QCString pumlExe = "java";
-  QCString pumlArgs = "-Djava.awt.headless=true -jar \""+plantumlJarPath+"plantuml.jar\" ";
+  QCString pumlArgs = "";
+
+  QStrList &pumlIncludePathList = Config_getList("PLANTUML_INCLUDE_PATH");
+  char *s=pumlIncludePathList.first();
+  if (s)
+  {
+    pumlArgs += "-Dplantuml.include.path=\"";
+    pumlArgs += s;
+    s = pumlIncludePathList.next(); 
+  }
+  while (s)
+  {
+    pumlArgs += portable_pathListSeparator();
+    pumlArgs += s;
+    s = pumlIncludePathList.next(); 
+  }
+  if (pumlIncludePathList.first()) pumlArgs += "\" ";
+  pumlArgs += "-Djava.awt.headless=true -jar \""+plantumlJarPath+"plantuml.jar\" ";
   pumlArgs+="-o \"";
   pumlArgs+=outDir;
   pumlArgs+="\" ";