--inject-checksum --force incorrectly removes comments from exts_list

[akesandgren]

diff from running inject-checksum --force

 exts_list = [
-    # note: more recent versions of setuptools (v34.x) can not be installed from source anymore,
-    # see https://github.com/pypa/setuptools/issues/980
     ('setuptools', '33.1.1', {

[boegel]

That may be a tricky one to fix...

There's also a related problem where comments above e.g. sources are getting moved around when --inject-checksums is used.

[verdurin]

I was just bitten by this one.