AUTH_PASSWORD_GENERATE event added

This is needed to replace the password generator by a plugin
implementation. Related to PR #166 and FS#2147
fixed syntax fuckup
Increased strength of auto generated passwords a bit

If you want better random initialization and more control over the
password strength install the passpolicy plugin.
Merge pull request #230 from splitbrain/pwgen-event

AUTH_PASSWORD_GENERATE event added