Allow lds==NULL on lam_output_open(), giving a default set of output

destinations (i.e., stderr)

This commit was SVN r1137.

src/util/output.c

@@ -328,6 +328,13 @@ static int do_open(int output_id, lam_output_stream_t *lds)
     i = output_id;
   }
 
+  /* Special case: if we got NULL for lds, then just use the default
+     verbose */
+
+  if (NULL == lds) {
+    lds = &verbose;
+  }
+
   /* Got a stream -- now initialize it and open relevant outputs */
 
   info[i].ldi_used = true;

src/util/output.h

@@ -220,6 +220,9 @@ extern "C" {
    * using it in successive calls to LAM_OUTPUT(), lam_output(),
    * lam_output_switch(), and lam_output_close().
    *
+   * If lds is NULL, the default descriptions will be used, meaning
+   * that output will only be sent to stderr.
+   *
    * It is safe to have multiple threads invoke this function
    * simultaneously; their execution will be serialized in an
    * unspecified manner.