Workaround Windows unpredictable file locking in Util.deleteContentsRecursive

Please enhance the hudson.Util.deleteContentsRecursive method to:

1. delete everything it can
2. try several times to delete everything
3. only throw an exception if it can't delete everything (listing everything that it can't delete)

Reasoning...
Unlike unix, the Microsoft Windows OS does not allow a file to be deleted if something has that file open. This causes delete operations to fail.
Furthermore, most installations of Windows have software that monitors the filesystem for activity and then inspects the contents of recently added/removed files (which means that it'll lock them, albeit temporarily), e.g. the Windows Search service & anti-virus software to name but two (but Windows Vista & Windows 7 seem to have additional complications)

This means that builds which rely on cleaning a workspace before they start will sometimes fail (claiming that they couldn't delete everything because a file was locked), resulting in a build failing with the following output:

Started by an SCM change
Building remotely on jenkinsslave27 in workspace C:\hudsonSlave\workspace\MyProject
Purging workspace...
hudson.util.IOException2: remote file operation failed: C:\hudsonSlave\workspace\MyProject at hudson.remoting.Channel@6f0564d7:jenkinsslave27
	at hudson.FilePath.act(FilePath.java:835)
	at hudson.FilePath.act(FilePath.java:821)
	at hudson.plugins.accurev.AccurevSCM.checkout(AccurevSCM.java:331)
	at hudson.model.AbstractProject.checkout(AbstractProject.java:1218)
	at hudson.model.AbstractBuild$AbstractRunner.checkout(AbstractBuild.java:586)
	at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:475)
	at hudson.model.Run.run(Run.java:1434)
	at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
	at hudson.model.ResourceController.execute(ResourceController.java:88)
	at hudson.model.Executor.run(Executor.java:239)
Caused by: java.io.IOException: Unable to delete C:\hudsonSlave\workspace\MyProject\...\src\...\foo - files in dir: [C:\hudsonSlave\workspace\MyProject\...\src\...\foo\bar]
	at hudson.Util.deleteFile(Util.java:236)
	at hudson.Util.deleteRecursive(Util.java:287)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.Util.deleteRecursive(Util.java:278)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.Util.deleteRecursive(Util.java:278)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.Util.deleteRecursive(Util.java:278)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.Util.deleteRecursive(Util.java:278)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.Util.deleteRecursive(Util.java:278)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.Util.deleteRecursive(Util.java:278)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.Util.deleteRecursive(Util.java:278)
	at hudson.Util.deleteContentsRecursive(Util.java:198)
	at hudson.plugins.accurev.PurgeWorkspaceContents.invoke(PurgeWorkspaceContents.java:28)
	at hudson.plugins.accurev.PurgeWorkspaceContents.invoke(PurgeWorkspaceContents.java:11)
	at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2161)
	at hudson.remoting.UserRequest.perform(UserRequest.java:118)
	at hudson.remoting.UserRequest.perform(UserRequest.java:48)
	at hudson.remoting.Request$2.run(Request.java:287)
	at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
	at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at hudson.remoting.Engine$1$1.run(Engine.java:60)
	at java.lang.Thread.run(Unknown Source)

What's needed is a retry mechanism. i.e. the equivalent of using Ant's <retry><delete file="foo"/></retry>, but with a (small) delay between attempts (and maybe a call to the garbage collector, just in case the process holding the file open is the build slave process itself).