New command GETEVENTCOUNTER.

* command.c (bump_key_eventcounter): New.
(bump_card_eventcounter): New.
(cmd_geteventcounter): New command.
* gpg-agent.c (handle_signal): Call bump_card_eventcounter.
* findkey.c (agent_write_private_key): Call bump_key_eventcounter.
* trustlist.c (agent_reload_trustlist): Ditto.

doc/gpg-agent.texi

@@ -657,6 +657,7 @@ secret keys.
 * Agent LEARN::           Register a smartcard
 * Agent PASSWD::          Change a Passphrase
 * Agent UPDATESTARTUPTTY:: Change the Standard Display
+* Agent GETEVENTCOUNTER:: Get the Event Counters
 @end menu
 
 @node Agent PKDECRYPT
@@ -1076,6 +1077,31 @@ to another screen.  It is only required because there is no way in the
 ssh-agent protocol to convey this information.
 
 
+@node Agent GETEVENTCOUNTER
+@subsection Get the Event Counters
+
+@example
+  GETEVENTCOUNTER
+@end example
+
+This function return one status line with the current values of the
+event counters.  The event counters are useful to avoid polling by
+delaying a poll until something has changed.  The values are decimal
+numbers in the range @code{0} to @code{UINT_MAX} and wrapping around to
+0.  The actual values should not be relied upon; they shall only be used
+to detect a change.
+
+The currently defined counters are are:
+@table @code
+@item ANY
+Incremented with any change of any of the other counters.
+@item KEY
+Incremented for added or removed private keys.
+@item CARD
+Incremented for changes of the card readers stati.
+@end table
+
+
 @mansect see also
 @ifset isman
 @command{gpg2}(1),