[JENKINS-21952] Resolve tags with slashes

If no revisions are found, try to use the branch as explicit reference.
This could be a tag rel/my-tags or any other explicit reference like a
gerrit changeset (refs/changes/xx/yy/z).
Trivial improvement

removed unncessary addAll call.
Fixed help and added docu for namespaced branches

See git-client-plugin Pull Request
https://github.com/jenkinsci/git-client-plugin/pull/120
Use BuildChooserContext environment in InverseBuildChooser

Fixes an issue introduced by 4fc7f4447c990082e8322c42ebafd1f33a2e60aa.

When polling git for changes, context.getBuild() returns null, manifesting in an NPE from  InverseBuildChooser.getCandidateRevisions() when polling a git repo and using an Inverse branch choosing strategy.

This was fixed for DefaultBuildChooser in 68331baf78649becac426b9362534faff08cf618--BuildChooserContext now includes the appropriate environment, so there is no longer any need to call context.getBuild().getEnvironment() as demonstrated in [DefaultBuildChooser.java](https://github.com/jenkinsci/git-plugin/commit/68331baf78649becac426b9362534faff08cf618#diff-59b21aee0282fdafd62036844373a19cL190).
Reverted wrong change regarding "any branch"
Switched to new git-client 1.6.4 containing namespace fix
Merge pull request #207 from alexanderlink/namespace-branch-help

Fixed help and added docu for namespaced branches
Fix to allow "remotes/origin/" in branch spec

https://issues.jenkins-ci.org/browse/JENKINS-20767
See comment:
https://issues.jenkins-ci.org/browse/JENKINS-20767?focusedCommentId=196575&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-196575
Added test for remotes/origin/ branches
Merge pull request #209 from alexanderlink/buildChooserFix

Fix to allow "remotes/origin/" in branch spec
Merge pull request #205 from pauxus/21952-tags-with-slashes

[JENKINS-21952] Resolve tags with slashes
Add test that a tag with a slash can be a branch spec
repository browser URL not saved
Test JENKINS-22604 - browser setting is lost when config is saved
Add Apache httpcomponents as a test time dependency

The new config round trip test fails without that test time dependency.
Merge pull request #211 from MarkEWaite/master-add-browser-url-round-trip-test

Test [Fixed JENKINS-22604] - browser setting is lost when config is saved
Enable use of trackingSubmodules

trackingSubmodules were introduced in v1.8.2 of GIT as a way to always
track the tip of the branch you are interested in for a submodule.  This
is turned on via the --remote switch to 'git submodule update'.  This
allows you to always stay up to date (--remote) or to just use the
specific SHA-1 you last downloaded (no --remote).

So, we now surface this new feature in the UI.  It requires corresponding
changes to the git-client-plugin (Pull request 122) for this to compile.
Use SubmoduleUpdateCommand

The SubmoduleUpdateCommand pattern allows for easier understanding of what each
of the parameters means.
Added sparse checkout option
Fixed Checkout command to act as the previous checkoutBranch method