No OOM in vim_strsave_escape_csi()
No OOM in concat_str() (few remaining cases)

Also fixed the duplicated declaration (path.c and strings.c)
No OOM in reverse_text()
No OOM in ExpandOldSetting()
Fix some "out of memory" comments and few cosmetics
No OOM for list_alloc()
Refator return logic in ses_put_fname()
Remove unnecessary comments and unnecessary return