[plt-scheme] PLT-Scheme 402 extension

> It used to be
>
> e2curve.dll
>
> but now it should be
>
> e2curve_ss.dll

Here is why, from /doc/release-notes/mzscheme/MzScheme_4.txt:

The naming convention for compiled files has changed to preserve
   the original file suffix. For example, the bytecode version of
   "x.ss" is now named "x_ss.zo". The "_loader" protocol for
   native-code extensions is no longer supported.