tree-wide: Convert to using autoptr(GString) vs g_string_free(...,TRUE)

If we're freeing the segment, it's basically always better to use
`autoptr()`.  Fewer lines, more reliable, etc.

Noticed an instance of this in the pull code while reviewing a different PR,
decided to do a grep for it and fix it tree wide.

Closes: #836
Approved by: pwithnall

src/libostree/ostree-bootloader-grub2.c

@@ -148,7 +148,7 @@ _ostree_bootloader_grub2_generate_config (OstreeSysroot                 *sysroot
                                           GError                       **error)
 {
   gboolean ret = FALSE;
-  GString *output = g_string_new ("");
+  g_autoptr(GString) output = g_string_new ("");
   g_autoptr(GOutputStream) out_stream = NULL;
   g_autoptr(GPtrArray) loader_configs = NULL;
   guint i;
@@ -260,8 +260,6 @@ _ostree_bootloader_grub2_generate_config (OstreeSysroot                 *sysroot
 
   ret = TRUE;
  out:
-  if (output)
-    g_string_free (output, TRUE);
   return ret;
 }
 

src/libostree/ostree-repo-commit.c

@@ -433,7 +433,7 @@ add_size_index_to_metadata (OstreeRepo        *self,
         {
           guint8 csum[OSTREE_SHA256_DIGEST_LEN];
           const char *e_checksum = sorted_keys->pdata[i];
-          GString *buffer = g_string_new (NULL);
+          g_autoptr(GString) buffer = g_string_new (NULL);
 
           ostree_checksum_inplace_to_bytes (e_checksum, csum);
           g_string_append_len (buffer, (char*)csum, sizeof (csum));
@@ -444,7 +444,6 @@ add_size_index_to_metadata (OstreeRepo        *self,
 
           g_variant_builder_add (&index_builder, "@ay",
                                  ot_gvariant_new_bytearray ((guint8*)buffer->str, buffer->len));
-          g_string_free (buffer, TRUE);
         }
       
       g_variant_builder_add (builder, "{sv}", "ostree.sizes",

src/libostree/ostree-repo-pull.c

@@ -3474,8 +3474,8 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
   bytes_transferred = _ostree_fetcher_bytes_transferred (pull_data->fetcher);
   if (bytes_transferred > 0 && pull_data->progress)
     {
-      guint shift; 
-      GString *buf = g_string_new ("");
+      guint shift;
+      g_autoptr(GString) buf = g_string_new ("");
 
       /* Ensure the rest of the progress keys are set appropriately. */
       update_progress (pull_data);
@@ -3499,7 +3499,6 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
                               (guint) ((end_time - pull_data->start_time) / G_USEC_PER_SEC));
 
       ostree_async_progress_set_status (pull_data->progress, buf->str);
-      g_string_free (buf, TRUE);
     }
 
   /* iterate over commits fetched and delete any commitpartial files */

src/libostree/ostree-repo.c

@@ -3717,7 +3717,6 @@ void
 ostree_repo_pull_default_console_progress_changed (OstreeAsyncProgress *progress,
                                                    gpointer             user_data)
 {
-  GString *buf;
   g_autofree char *status = NULL;
   gboolean scanning;
   guint outstanding_fetches;
@@ -3729,7 +3728,7 @@ ostree_repo_pull_default_console_progress_changed (OstreeAsyncProgress *progress
   guint fetched_delta_part_fallbacks;
   guint total_delta_part_fallbacks;
 
-  buf = g_string_new ("");
+  g_autoptr(GString) buf = g_string_new ("");
 
   ostree_async_progress_get (progress,
                              "outstanding-fetches", "u", &outstanding_fetches,
@@ -3838,8 +3837,6 @@ ostree_repo_pull_default_console_progress_changed (OstreeAsyncProgress *progress
     }
 
   glnx_console_text (buf->str);
-
-  g_string_free (buf, TRUE);
 }
 
 /**