[FIXED JENKINS-13154] AnnotationMapper bug was causing massive lock contention when saving fingerprints.

Prevents us from leaving behind a temp dir with cyclic symlinks, which breaks JGit’s clean function.
That in turn can cause test builds to break:
https://jenkins.ci.cloudbees.com/job/core/job/jenkins_main_trunk/783/console
Cleaning workspace
FATAL: Could not delete file …/workspace/core/jenkins_main_trunk/core/target/hudson5309354136960541268tmp/c/symlink/c/symlink/c/symlink/…/c/foo.xml
org.eclipse.jgit.api.errors.JGitInternalException: Could not delete file …/workspace/core/jenkins_main_trunk/core/target/hudson5309354136960541268tmp/c/symlink/c/symlink/c/symlink/…/c/foo.xml
	at org.eclipse.jgit.api.CleanCommand.call(CleanCommand.java:137)
	at org.jenkinsci.plugins.gitclient.JGitAPIImpl.clean(JGitAPIImpl.java:305)
	at hudson.plugins.git.GitAPI.clean(GitAPI.java:248)
	at hudson.plugins.git.GitSCM$4.invoke(GitSCM.java:1213)
	at hudson.plugins.git.GitSCM$4.invoke(GitSCM.java:1196)
	at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2236)
	at hudson.remoting.UserRequest.perform(UserRequest.java:118)
	at hudson.remoting.UserRequest.perform(UserRequest.java:48)
	at hudson.remoting.Request$2.run(Request.java:326)
	at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:722)
Caused by: java.io.IOException: Could not delete file …/workspace/core/jenkins_main_trunk/core/target/hudson5309354136960541268tmp/c/symlink/c/symlink/c/symlink/…/c/foo.xml
	at org.eclipse.jgit.util.FileUtils.delete(FileUtils.java:142)
	at org.eclipse.jgit.util.FileUtils.delete(FileUtils.java:126)
	at org.eclipse.jgit.util.FileUtils.delete(FileUtils.java:126)
	…
	at org.eclipse.jgit.util.FileUtils.delete(FileUtils.java:126)
	at org.eclipse.jgit.util.FileUtils.delete(FileUtils.java:126)
	at org.eclipse.jgit.api.CleanCommand.call(CleanCommand.java:132)
	... 14 more

'mvn -Dtest=hudson.maven.MavenProjectTest#testDeleteSetBuildDeletesModuleBuilds test' fails on empty local repo.
~/.m2/repository/org/jvnet/hudson/main/test/multimod/moduleA/1.0-SNAPSHOT/moduleA-1.0-SNAPSHOT.jar was missing; need install goal.
Better to set a local repo so we do not pollute the real repo, and to avoid interaction between tests.

This code was borked as SlaveComputer is not serializable and we are passing an implicit ref to the outer class.

- I suspect that nobody has ever used this method given the lack of conversion to static inner class required to make it work

f43cde68.

${rootURL} should be used to locate env-vars.html, since otherwise the link will be broken when the builder is configured from a job inside a folder.

[FIXED JENKINS-10502] Option to make the build not fail if there is nothing to archive

[FIXED JENKINS-17177] wrong build result in post build steps after failed pre build step in maven project

based on the conversation with Weltraumschaf (the DARCS plugin maintainer)

Generally the environment is responsible for imposing a general timeout on tests.
And this timeout makes debugging more difficult.