Die with a useful error if we can't connect to the logging DB

Instead of dying later with a message about prepare failing
Print a warning when terminating instead of dying immediately

This way, the warning message is more likely to be seen than it it were mixed
in with the program's output at the beginning.
Updated `genome` tab completion.
Updated `gmt` tab completion.
Merge pull request #277 from brummett/logging_db

Die with a useful error if we can't connect to the logging DB