"node rejoin": actively check for node to rejoin cluster

Previously repmgr was relying on whatever command was configured to
start PostgreSQL to determine whether the node being rejoined had
started correctly. However it's preferable to actively poll the upstream
to confirm it has restarted and actually attached as a standby before
confirming success of the "node rejoin" action.

This can be overridden with the -W/--no-wait option.

(Note that for consistency with other PostgreSQL utilities, the
short form of the --wait option is now "-w"; this is currently
only used in "repmgr standby follow".)

Also update "repmgr node rejoin" documentation with a list of supported
options, and add some useful index entries for "pg_rewind".

Implements GitHub #415.

doc/switchover.sgml

@@ -180,6 +180,10 @@
    </note>
 
   <sect2 id="switchover-pg-rewind" xreflabel="Switchover and pg_rewind">
+    <indexterm>
+      <primary>pg_rewind</primary>
+      <secondary>using with "repmgr standby switchover"</secondary>
+    </indexterm>
     <title>Switchover and pg_rewind</title>
     <para>
       If the demotion candidate does not shut down smoothly or cleanly, there's a risk it
@@ -206,7 +210,7 @@
     </para>
     <para>
       <application>pg_rewind</application> has been part of the core PostgreSQL distribution since
-      version 9.5. Users of versions 9.3 and 9.4 will need to manually install; source code available here:
+      version 9.5. Users of versions 9.3 and 9.4 will need to manually install it; the source code is available here:
       <ulink url="https://github.com/vmware/pg_rewind">https://github.com/vmware/pg_rewind</ulink>.
       If the <application>pg_rewind</application>
       binary is not installed in the PostgreSQL <filename>bin</filename> directory, provide