Problem: some patterns are used as a replacement for one-two explicit
file matches (like '^[mM]akefile$'). As matching file name directly is
faster and more explicit, it should be preferred.
Solution: move those patterns to direct file name match.
NOTE: this is not strictly backwards compatible, because exact file
name matching is done *before* pattern matching. If user has
conflicting `vim.filetype.add()` call with high priority (like with
`pattern='file$'` and `priority=100`), after this change it will be
ignored (i.e. 'makefile' will match exactly).
Judging by converted cases, it seems reasonable to prefer exact
matches there.
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