The license was originally MIT, but when this module became part of systemd,
it was changed to LGPLv2+. All files had correct headers, so only the LICENSE
file needs updating. Take the opportunity to add classifiers to setup.py.

In practice this shouldn't make much difference, but
sometimes our headers might be newer, and we want to
test them.

In trying to track down a stupid linker bug, I noticed a bunch of
memset() calls that should be using memzero() to make it more "obvious"
that the options are correct (i.e. 0 is not the length, but the data to
set).  So fix up all current calls to memset(foo, 0, length) to
memzero(foo, length).

- separate methods with two empty lines for clarity
- avoid malloc(0) by specyfing private data size as -1
- add method name in error messages