core: Make ot_transfer_out_value() take a & for the second argument

As Ray Strode argued, it's confusing to have something that looks like
a function be magical.  And OT_TRANSFER_OUT_VALUE is uglier.

src/libotutil/ot-gio-utils.c

@@ -188,7 +188,7 @@ ot_gio_splice_and_checksum (GOutputStream  *out,
     }
 
   ret = TRUE;
-  ot_transfer_out_value(out_checksum, ret_checksum);
+  ot_transfer_out_value(out_checksum, &ret_checksum);
  out:
   ot_clear_checksum (&ret_checksum);
   return ret;

src/libotutil/ot-unix-utils.c

@@ -67,7 +67,7 @@ ot_util_spawn_pager (GOutputStream  **out_stream,
       ret_stream = (GOutputStream*)g_unix_output_stream_new (stdin_fd, TRUE);
     }
 
-  ot_transfer_out_value(out_stream, ret_stream);
+  ot_transfer_out_value(out_stream, &ret_stream);
   ret = TRUE;
  out:
   g_clear_object (&ret_stream);
@@ -149,7 +149,7 @@ ot_util_path_split_validate (const char *path,
     }
 
   ret = TRUE;
-  ot_transfer_out_value(out_components, ret_components);
+  ot_transfer_out_value(out_components, &ret_components);
  out:
   if (ret_components)
     g_ptr_array_unref (ret_components);

src/libotutil/ot-variant-utils.c

@@ -114,7 +114,7 @@ ot_util_variant_map (GFile *src,
   g_variant_ref_sink (ret_variant);
   
   ret = TRUE;
-  ot_transfer_out_value(out_variant, ret_variant);
+  ot_transfer_out_value(out_variant, &ret_variant);
  out:
   ot_clear_gvariant (&ret_variant);
   if (mfile)

src/libotutil/otutil.h

@@ -35,8 +35,8 @@
 #define ot_transfer_out_value(outp, srcp) G_STMT_START {   \
   if (outp)                                                \
     {                                                      \
-      *outp = srcp;                                        \
-      srcp = NULL;                                         \
+      *outp = *srcp;                                       \
+      *(srcp) = NULL;                                      \
     }                                                      \
   } G_STMT_END;