Avoid problem reading jni.h on Macs.

Apple released an update recently in which there
was a broken symlink for jni.h that pointed to
a non-existent file. CMake had trouble configuring
because it encountered an error trying to read
jni.h.

We avoid the problem here by introducing a variable
CTEST_RUN_Java, which defaults to OFF on Macs, that
indicates whether to even attempt finding java, reading
jni.h and adding the "Java" CMake test.

If you would like to test Java on a Mac where the
jni.h symlink is not busted, feel free to pass in
-DCTEST_RUN_Java:BOOL=ON when configuring CMake.

Tests/CMakeLists.txt

@@ -1635,7 +1635,15 @@ ${CMake_BINARY_DIR}/bin/cmake -DVERSION=master -P ${CMake_SOURCE_DIR}/Utilities/
     ENDIF()
   ENDIF()
 
-  IF(NOT CMAKE_TEST_GENERATOR MATCHES "Xcode")
+  if(NOT DEFINED CTEST_RUN_Java)
+    if(APPLE)
+      set(CTEST_RUN_Java OFF)
+    else()
+      set(CTEST_RUN_Java ON)
+    endif()
+  endif()
+
+  IF(CTEST_RUN_Java)
     find_package(Java QUIET)
     IF(JAVA_COMPILE AND JAVA_RUNTIME AND JAVA_ARCHIVE AND NOT MINGW)
       GET_FILENAME_COMPONENT(JNIPATH ${JAVA_COMPILE} PATH)
@@ -1659,7 +1667,7 @@ ${CMake_BINARY_DIR}/bin/cmake -DVERSION=master -P ${CMake_SOURCE_DIR}/Utilities/
         ENDIF("${JNI_FILE}" MATCHES "JDK1_2")
       ENDIF(JNI_H)
     ENDIF(JAVA_COMPILE AND JAVA_RUNTIME AND JAVA_ARCHIVE AND NOT MINGW)
-  ENDIF(NOT CMAKE_TEST_GENERATOR MATCHES "Xcode")
+  ENDIF(CTEST_RUN_Java)
 
   # add some cross compiler tests, for now only with makefile based generators
   IF(CMAKE_TEST_GENERATOR MATCHES "Makefiles" OR CMAKE_TEST_GENERATOR MATCHES "KDevelop")