DOC: fix a few typos

include/types/proto_http.h: hwen -> when
include/types/server.h: SRV_ST_DOWN -> SRV_ST_STOPPED
src/backend.c: prefer-current-server -> prefer-last-server

Signed-off-by: Godbach <nylzhaowei@gmail.com>
diff --git a/include/types/proto_http.h b/include/types/proto_http.h
index 95bf59d..2654b78 100644
--- a/include/types/proto_http.h
+++ b/include/types/proto_http.h
@@ -71,7 +71,7 @@
 
 /* indicate how we *want* the connection to behave, regardless of what is in
  * the headers. We have 4 possible values right now :
- * - WANT_KAL : try to maintain keep-alive (default hwen nothing configured)
+ * - WANT_KAL : try to maintain keep-alive (default when nothing configured)
  * - WANT_TUN : will be a tunnel (CONNECT).
  * - WANT_SCL : enforce close on the server side
  * - WANT_CLO : enforce close on both sides
diff --git a/include/types/server.h b/include/types/server.h
index 4847def..1cabb83 100644
--- a/include/types/server.h
+++ b/include/types/server.h
@@ -43,7 +43,7 @@
 #include <types/checks.h>
 
 
-/* server states. Only SRV_ST_DOWN indicates a down server. */
+/* server states. Only SRV_ST_STOPPED indicates a down server. */
 enum srv_state {
 	SRV_ST_STOPPED = 0,              /* the server is down. Please keep set to zero. */
 	SRV_ST_STARTING,                 /* the server is warming up (up but throttled) */