UseSWIG: Record generated java files as custom command outputs

When another target depends on the generated files CMake must know which
custom command generates them in order to hook up the dependency
properly.  We already do this for Python.  Add the Java files too.

Modules/UseSWIG.cmake

@@ -57,7 +57,8 @@
 set(SWIG_CXX_EXTENSION "cxx")
 set(SWIG_EXTRA_LIBRARIES "")
 
-set(SWIG_PYTHON_EXTRA_FILE_EXTENSION "py")
+set(SWIG_PYTHON_EXTRA_FILE_EXTENSIONS ".py")
+set(SWIG_JAVA_EXTRA_FILE_EXTENSIONS ".java" "JNI.java")
 
 #
 # For given swig module initialize variables associated with it
@@ -123,9 +124,9 @@ macro(SWIG_GET_EXTRA_OUTPUT_FILES language outfiles generatedpath infile)
     endif ()
 
   endif()
-  foreach(it ${SWIG_${language}_EXTRA_FILE_EXTENSION})
+  foreach(it ${SWIG_${language}_EXTRA_FILE_EXTENSIONS})
     set(${outfiles} ${${outfiles}}
-      "${generatedpath}/${SWIG_GET_EXTRA_OUTPUT_FILES_module_basename}.${it}")
+      "${generatedpath}/${SWIG_GET_EXTRA_OUTPUT_FILES_module_basename}${it}")
   endforeach()
 endmacro()