tree: Fix various typos and outdated terminology

This was mostly machine generated with the following command:
```
codespell \
    --builtin clear,rare,usage \
    --skip './po/*' --skip './.git/*' --skip './NEWS*' \
    --write-changes .
```
using the latest git version of `codespell` as per [these
instructions](https://github.com/codespell-project/codespell#user-content-updating).

Then I manually checked each change using `git add -p`, made a few
manual fixups and dropped a load of incorrect changes.

There are still some outdated or loaded terms used in GLib, mostly to do
with git branch terminology. They will need to be changed later as part
of a wider migration of git terminology.

If I’ve missed anything, please file an issue!

Signed-off-by: Philip Withnall <withnall@endlessm.com>

gio/kqueue/gkqueuefilemonitor.c

@@ -354,7 +354,7 @@ g_kqueue_file_monitor_callback (gint fd, GIOCondition condition, gpointer user_d
              * rescan of missing files immediately so we don't have to wait for
              * 4 seconds for discovering missing files. We pass the sub_file
              * corresponding to the GKqueueFileMonitor to 'check_this_sub_only'
-             * argument to prevent _km_scan_missing from emiting 'CREATED'
+             * argument to prevent _km_scan_missing from emitting 'CREATED'
              * events because _kh_dir_diff will do it for us. */
             if (sub->mon->sub_file != NULL && sub->mon->sub_file->fd == -1)
               _km_scan_missing (sub->mon->sub_file);