Improve debugging and add PERROR call

Add three level of verbosity with DBG, DBG2 and DBG3.

Each perror() call from now on should use PERROR().

Migration to these new debug facilities will come later on and
progressively.

To increase debug level use -v, -vv and -vvv respectively.

Signed-off-by: David Goulet <david.goulet@polymtl.ca>