Parse and put into effect this buffer's local variables spec.
Uses `hack-local-variables-apply' to apply the variables.
If MODE-ONLY is non-nil, all we do is check whether a "mode:"
is specified, and return the corresponding mode symbol, or nil.
In this case, we try to ignore minor-modes, and only return a
major-mode.
If `enable-local-variables' or `local-enable-local-variables' is nil,
this function does nothing. If `inhibit-local-variables-regexps'
applies to the file in question, the file is not scanned for
local variables, but directory-local variables may still be applied.