Patch from Armin Rigo.

Also, don't run it if 'gui' is not requested.  Patch by Xiang Zhang.

Issue 27921: Remove backslash from another f-string. I'll revert this change before beta 2. I also need to look in to why test_tools/test_unparse fails with the files that are now being skipped.

Issue #11734: Add support for IEEE 754 half-precision floats to the struct module. Original patch by Eli Stevens.

Closes issue 27921: Disallow backslashes anywhere in f-strings. This is a temporary restriction. In 3.6 beta 2, the plan is to again allow backslashes in the string parts of f-strings, but disallow them in the expression parts.

Add also a newline for readability in normalize_encoding().