Fixes setting the verbosity for AGMG.

If verbosity is true, we set the iprint parameter such that the
output is print to standard out. If not, we use a negative number
such that only error messages are printed to standard out.
Merge pull request #277 from blattms/fix-agmg-verbosity

Fixes setting the verbosity for AGMG.
Merge remote-tracking branch 'upstream/master'