BUG/MINOR: force-persist and ignore-persist only apply to backends

>From the very first day of force-persist and ignore-persist features,
they only applied to backends, except that the documentation stated it
could also be applied to frontends.

In order to make it clear, the documentation is updated and the parser
will raise a warning if the keywords are used in a frontend section.

This patch should be backported up to the 1.5 branch.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index a914c41..992e18a 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -2039,7 +2039,7 @@
 errorloc302                               X          X         X         X
 -- keyword -------------------------- defaults - frontend - listen -- backend -
 errorloc303                               X          X         X         X
-force-persist                             -          X         X         X
+force-persist                             -          -         X         X
 filter                                    -          X         X         X
 fullconn                                  X          -         X         X
 grace                                     X          X         X         X
@@ -2052,7 +2052,7 @@
 http-reuse                                X          -         X         X
 http-send-name-header                     -          -         X         X
 id                                        -          X         X         X
-ignore-persist                            -          X         X         X
+ignore-persist                            -          -         X         X
 load-server-state-from-file               X          -         X         X
 log                                  (*)  X          X         X         X
 log-format                                X          X         X         -
@@ -3503,7 +3503,7 @@
 force-persist { if | unless } <condition>
   Declare a condition to force persistence on down servers
   May be used in sections:    defaults | frontend | listen | backend
-                                  no   |    yes   |   yes  |   yes
+                                  no   |    no    |   yes  |   yes
 
   By default, requests are not dispatched to down servers. It is possible to
   force this using "option persist", but it is unconditional and redispatches
@@ -4825,7 +4825,7 @@
 ignore-persist { if | unless } <condition>
   Declare a condition to ignore persistence
   May be used in sections:    defaults | frontend | listen | backend
-                                  no   |    yes   |   yes  |   yes
+                                  no   |    no    |   yes  |   yes
 
   By default, when cookie persistence is enabled, every requests containing
   the cookie are unconditionally persistent (assuming the target server is up
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 27d7eee..c40e71d 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -4068,7 +4068,7 @@
 			goto out;
 		}
 
-		if (warnifnotcap(curproxy, PR_CAP_FE|PR_CAP_BE, file, linenum, args[0], NULL))
+		if (warnifnotcap(curproxy, PR_CAP_BE, file, linenum, args[0], NULL))
 			err_code |= ERR_WARN;
 
 		if (strcmp(args[1], "if") != 0 && strcmp(args[1], "unless") != 0) {