[PATCH] Fix parameter type in C++ version of iseqsig (bug 23171)

[Gabriel F. T. Gomes]

On Mon, 14 May 2018, Gabriel F. T. Gomes wrote:

>mistakenly used double parameters in the long double version of iseqsig,
>thus causing spurious conversions to double, as reported on bug 23171.

By the way, is there any kind of test, which could be added to the test
suite, and that would have detected such spurious conversions?