DOC: Spelling fixes

[wt: this contains spelling fixes for both doc and code comments,
 should be backported, ignoring the parts which don't apply]
diff --git a/src/proto_uxst.c b/src/proto_uxst.c
index b2a7fe2..5c8f9d4 100644
--- a/src/proto_uxst.c
+++ b/src/proto_uxst.c
@@ -407,7 +407,7 @@
  *  - SF_ERR_PRXCOND if the connection has been limited by the proxy (maxconn)
  *  - SF_ERR_RESOURCE if a system resource is lacking (eg: fd limits, ports, ...)
  *  - SF_ERR_INTERNAL for any other purely internal errors
- * Additionnally, in the case of SF_ERR_RESOURCE, an emergency log will be emitted.
+ * Additionally, in the case of SF_ERR_RESOURCE, an emergency log will be emitted.
  *
  * The connection's fd is inserted only when SF_ERR_NONE is returned, otherwise
  * it's invalid and the caller has nothing to do.