Check user pattern for MessageExclusion extension

Either it can throw exception during polling:

Failed to record SCM polling for hudson.model.FreeStyleProject@29de87b6[JobName]
java.util.regex.PatternSyntaxException: Dangling meta character '*' near index 0
*
^
	at java.util.regex.Pattern.error(Pattern.java:1924)
	at java.util.regex.Pattern.sequence(Pattern.java:2090)
	at java.util.regex.Pattern.expr(Pattern.java:1964)
	at java.util.regex.Pattern.compile(Pattern.java:1665)
	at java.util.regex.Pattern.<init>(Pattern.java:1337)
	at java.util.regex.Pattern.compile(Pattern.java:1022)
	at hudson.plugins.git.extensions.impl.MessageExclusion.isRevExcluded(MessageExclusion.java:41)
	at hudson.plugins.git.GitSCM.isRevExcluded(GitSCM.java:1485)
	at hudson.plugins.git.GitSCM.compareRemoteRevisionWithImpl(GitSCM.java:584)
	at hudson.plugins.git.GitSCM.compareRemoteRevisionWith(GitSCM.java:494)
	at hudson.scm.SCM._compareRemoteRevisionWith(SCM.java:357)
	at hudson.scm.SCM.poll(SCM.java:374)
	at org.jenkinsci.plugins.multiplescms.MultiSCM.compareRemoteRevisionWith(MultiSCM.java:92)
	at hudson.scm.SCM._compareRemoteRevisionWith(SCM.java:357)
	at hudson.scm.SCM.poll(SCM.java:374)
	at hudson.model.AbstractProject.pollWithWorkspace(AbstractProject.java:1449)
	at hudson.model.AbstractProject._poll(AbstractProject.java:1420)
	at hudson.model.AbstractProject.poll(AbstractProject.java:1331)
	at hudson.triggers.SCMTrigger$Runner.runPolling(SCMTrigger.java:477)
	at hudson.triggers.SCMTrigger$Runner.run(SCMTrigger.java:506)
	at hudson.util.SequentialExecutionQueue$QueueEntry.run(SequentialExecutionQueue.java:118)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
	at java.util.concurrent.FutureTask.run(FutureTask.java:262)
	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:745)
Merge pull request #282 from KostyaSha/commit_exclusion

Check user pattern for MessageExclusion extension