Fix duplicate IDs

Asciidoctor automatically creates an anchor "_git_p4"for the "Git-p4"
section in client-p4.asc which is the same as the anchor explicitly
defined in import-p4.asc. This is the same case for "_task_lists" in
2-contributing.asc and "_audit_log" in 4-managing-organization.
http://asciidoctor.org/docs/user-manual/#automatic-anchors

Author: yunhailuo

book/06-github/sections/2-contributing.asc

@@ -313,9 +313,9 @@ You can create a task list like this:
 - [ ] Document the code
 ----
 
-If we include this in the description of our Pull Request or Issue, we'll see it rendered like <<_task_lists>>
+If we include this in the description of our Pull Request or Issue, we'll see it rendered like <<_eg_task_lists>>
 
-[[_task_lists]]
+[[_eg_task_lists]]
 .Task lists rendered in a Markdown comment.
 image::images/markdown-02-tasks.png[Example Task List]
 

book/06-github/sections/4-managing-organization.asc

@@ -65,7 +65,7 @@ Special-interest teams like `ux`, `css`, or `refactoring` are useful for certain
 Organizations also give owners access to all the information about what went on under the organization.
 You can go to the 'Audit Log' tab and see what events have happened at an organization level, who did them and where in the world they were done.
 
-[[_audit_log]]
+[[_the_audit_log]]
 .The Audit log.
 image::images/orgs-03-audit.png[]
 

book/09-git-and-other-scms/sections/client-p4.asc

@@ -312,6 +312,7 @@ You can even use Git submodules (though they'll look strange to Perforce users),
 
 If you can't convince the administrator of your server to set up Git Fusion, there is still a way to use these tools together.
 
+[[_git_p4_client]]
 ===== Git-p4
 
 (((git commands, p4)))