Ensure all build steps have examples

Deprecate the undocumented P4Sync step

master/NEWS

@@ -41,6 +41,9 @@ addChange(). This lets the buildmaster know which VCS the Change is coming
 from, such as 'git' or 'svn'. This means that you need to use the version
 of your contrib script that corresponds to your buildmaster.
 
+*** The un-documented P4Sync source step has been deprecated and will be
+removed in the next version.
+
 ** Customizable validation regexps
 
 The global c['validation'] parameter can be used to adjust the regular

master/buildbot/steps/source/oldsource.py

@@ -1307,7 +1307,10 @@ def startVC(self, branch, revision, patch):
         self.startCommand(cmd)
 
 class P4Sync(Source):
-    """This is a partial solution for using a P4 source repository. You are
+    """
+    DEPRECATED - will be removed in 0.8.5.
+    
+    This is a partial solution for using a P4 source repository. You are
     required to manually set up each build slave with a useful P4
     environment, which means setting various per-slave environment variables,
     and creating a P4 client specification which maps the right files into