The build fails (not everytime) when including the apisupport module.  For
example, with a fresh extraction of NetBeans-release31-13-src.zip and NetBeans-
release31-13-extbin.zip and on executing the command:
    ant -Dmoduleconfig=stable-with-apisupport
the following error message is displayed:
[exec] compile:
     [exec]     [javac] Compiling 58 source files to F:\sunbeans\netbeans-
src\apisupport\src
     [exec]     [javac] F:\sunbeans\netbeans-
src\apisupport\src\org\netbeans\modules\apisupport\CompilerTypeTester.java:114:
cannot access org.openide.util.Task
     [exec]     [javac] file org\openide\util\Task.class not found
     [exec]     [javac]                 if (job.start ().isSuccessful ())
     [exec]     [javac]                               ^
     [exec]     [javac] F:\sunbeans\netbeans-
src\apisupport\src\org\netbeans\modules\apisupport\ExecutorTester.java:106:
inconvertible types
     [exec]     [javac] found   : java.lang.Object
     [exec]     [javac] required: org.openide.execution.ExecutorTask
     [exec]     [javac]                 int result = ((ExecutorTask) m.invoke
(exec, new Object[] { testInfo })).result ();
     [exec]     [javac]                                                       ^
     [exec]     [javac] Note: Some input files use or override a deprecated API.
     [exec]     [javac] Note: Recompile with -deprecation for details.
     [exec]     [javac] 2 errors
     [exec]
     [exec] Total time: 2 minutes 35 seconds

On executing it again the build suceeds.