Update copyright strings

Thanks to Jerome Benoit
Silence module detection warning when not loading

The warning says that we will always load the modules, even though we
will honour the variable which says never to do so.

Thanks to Jerome Benoit
Treat mktemp like other required commands

Add it to configure script and use the which_cmd to detect at runtime.

Thanks to Jerome Benoit
Don't delete and recreate the temporary directory

mktemp already ensured it was unique as part of creating it

Thanks to Jerome Benoit
Use mktemp for temporary directories during RPC

Slightly safer than random numbers because it can never conflict

Thanks to Jerome Benoit
Remove redundant firehol_wget and wget_cmd helpers

They were used by ecn_shame only, which was removed some time back since
the list is no longer available.

Thanks to Jerome Benoit