got broken to the previous array cleanup and grepping struct
definition only from headers.

Instead of having a null pointer, use a dummy array which just
says the array is empty. This helps in multiple places of the code
which would otherwise need explicitly need to check first if the
array exists. This has been cause of multiple seg.faults in the
past as the array check is easily omitted.

This also removes (or fixes) all existing checks accordingly.

clean up the triggers properly, in proper order.

especially important if the package requested from command line
does not exist. otherwise we would not print an error at all.

Print more information why installation changeset calculation failed.
Fixes #187.

To print upgrading if package is actually being changed instead of
pure reinstall.

If version is equal, but package contents are different we should
show the package being upgraded.