Trying to improve performance of getTags.
· Retrieving DIRENT_TIME rather than DIRENT_ALL since we are only using the date (and name) fields.
· Making isSVNRepositoryProjectRoot short-circuit to false when we are not in fact in the project root.
Nonetheless it remains ~6× slower than a simple CLI svn ls https://github.com/kohsuke/groovy-sandbox/tags command:
"Handling GET /job/…/build : …
   java.lang.Thread.State: RUNNABLE
	at java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
	- locked <0x00000000f5cd9118> (a java.net.SocksSocketImpl)
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
	at java.net.Socket.connect(Socket.java:579)
	at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:618)
	at org.tmatesoft.svn.core.internal.util.SVNSocketFactory.connect(SVNSocketFactory.java:146)
	at org.tmatesoft.svn.core.internal.util.SVNSocketFactory.createSSLSocket(SVNSocketFactory.java:106)
	at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.connect(HTTPConnection.java:280)
	at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection._request(HTTPConnection.java:451)
	at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:382)
	at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:373)
	at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:361)
	at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.performHttpRequest(DAVConnection.java:707)
	at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.exchangeCapabilities(DAVConnection.java:627)
	at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.open(DAVConnection.java:102)
	at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.openConnection(DAVRepository.java:1020)
	at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.getLatestRevision(DAVRepository.java:180)
	at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgRepositoryAccess.getRevisionNumber(SvnNgRepositoryAccess.java:118)
	at org.tmatesoft.svn.core.internal.wc2.SvnRepositoryAccess.getLocations(SvnRepositoryAccess.java:148)
	at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgRepositoryAccess.createRepositoryFor(SvnNgRepositoryAccess.java:45)
	at org.tmatesoft.svn.core.internal.wc2.remote.SvnRemoteList.run(SvnRemoteList.java:42)
	at org.tmatesoft.svn.core.internal.wc2.remote.SvnRemoteList.run(SvnRemoteList.java:34)
	at org.tmatesoft.svn.core.internal.wc2.SvnOperationRunner.run(SvnOperationRunner.java:20)
	at org.tmatesoft.svn.core.wc2.SvnOperationFactory.run(SvnOperationFactory.java:1238)
	at org.tmatesoft.svn.core.wc2.SvnOperation.run(SvnOperation.java:294)
	at org.tmatesoft.svn.core.wc.SVNLogClient.doList(SVNLogClient.java:1307)
	at hudson.scm.listtagsparameter.ListSubversionTagsParameterDefinition.getTags(ListSubversionTagsParameterDefinition.java:198)
Changed tag listing to run asynchronously and populate the pulldown when it could.
Besides the obvious responsiveness improvement in the UI,
this avoids calling getTags 4× or more per page load due to lack of a local variable caching ${it.tags} (!).
Better handling of errors loading tags.
Removing comment which is better filed as JENKINS-21701.
Minor tweaks to getTags method.
Merge branch 'master' into ListSubversionTagsParameterDefinition-performance

Conflicts:
	src/main/java/hudson/scm/listtagsparameter/ListSubversionTagsParameterDefinition.java
	src/test/java/hudson/scm/listtagsparameter/ListSubversionTagsParameterDefinitionTest.java
Forgot to commit rest of merge resolution. Git is annoying.
Merge pull request #67 from jglick/ListSubversionTagsParameterDefinition-performance

List Subversion Tags parameter definition performance