Extend a docstring.
Use a somewhat nicer touch.

It doesn't wipe the content of .itime and .import_error files
in the (admittedly strange) case there is something interesting
inside.
YamlLoader: add gen/GEN among the files to be checked for changes.

It is inspected to build subtasks.
Typos.
Removed length and binary response in the fake remote service.

The real remote service in async library changed (binary response was
unused, thus also the message length became unnecessary). The fake
remote service (implemented in cmstestsuite) needs to account for
those changes. For the tests to continue working.
Added some files to the installation to fix cmstestsuite.