Give access to job size to the plugins + enhancements/corrections

The JobBytes, ReadBytes and LastRate values were not available to the
plugins of the Director.

Also, since the plugin needs to know about Canceled jobs, I moved the
is_job_canceled() function after it passed through the plugins.

While testing my changes, I came unto a signed/unsigned problem with
values >2^31 (0000002:0000002,100,000,000). Python does not sign its
integers so when passing an unsigned value to Python, it needs to be
made explicitly. I added a function to correctly send the added
variables (JobBytes, ReadBytes and LastRate) to Python as unsigned but I
also moved some variables sent as signed integer to Python while they
may be over 2^31 to that function (*JobFiles and *Errors) since they are
defined as unsigned in the C code.

Fixes #334: Give access to job size to the plugins +
            enhancements/corrections

Signed-off-by: Marco van Wieringen <marco.van.wieringen@bareos.com>
Miss casts and zeroing of integers
Fix wrong sanity check.

When comparing if we use the same read and write storage in migrations
and copies we should ignore any autochanger devices as its fine to use
those as both read and write device.
Revert removal of POOL_MEM::max_size method.
Inherit base class from object

By inheriting from object, it becomes a so calles "new style" class in
python, which is common nowadays, and also default in python 3.x

Signed-off-by: Marco van Wieringen <marco.van.wieringen@bareos.com>
Update AUTHORS.