Rework the R16B03 syntax_tools bug workaround better

I found a way to improve the parse transform to work also in the
presence of the syntax tools bug in Erlang/OTP R16B03, and still
keep the natural way of writing local implicit funs: like "fun x/1",
thus no longer any need to rewrite the other code in the module that
uses the parse transform.
Prepare for 3.7.1