DOC: fix name for "option independant-streams"

The correct spelling is "independent", not "independant". This patch
fixes the doc and the configuration parser to accept the correct form.
The config parser still allows the old naming for backwards compatibility.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 53dd96d..c93edd2 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -119,7 +119,7 @@
 #define PR_O2_RDPC_PRST	0x00000200      /* Actvate rdp cookie analyser */
 #define PR_O2_CLFLOG	0x00000400      /* log into clf format */
 #define PR_O2_LOGHCHKS	0x00000800	/* log health checks */
-#define PR_O2_INDEPSTR	0x00001000	/* independant streams, don't update rex on write */
+#define PR_O2_INDEPSTR	0x00001000	/* independent streams, don't update rex on write */
 #define PR_O2_SOCKSTAT	0x00002000	/* collect & provide separate statistics for sockets */
 
 /* appsession */