Module revamp

I really like this little module, and I'd like to help maintain it. Or at least, permit me to submit a patch which should solve several outstanding tickets at once (plus a few I found myself). Since the patch is so big and changes a LOT, I've also just included a drop-in replacement of genpass.module. Here's what it includes:

- I changed some of the coding style to make Coder happy.

- I added LOTS of documentation.

- I used defines for the genpass_mode options (easier to remember what modes mean throughout the code). These are GENPASS_DEFAULT, GENPASS_OPTIONAL, AND GENPASS_RESTRICTED.

- When the user cannot choose a password, I changed from a hidden password field (which can be manipulated), to restricting access via #access = FALSE.

- I consolidated the two user registration validation functions, to reduce duplicate code.

- I also removed the genpass_user_admin_settings_submit() function, since everything in it was unnecessary. All the settings included in the user settings form get saved automatically by system_settings_form().

- I added the following confirmation message if the password is optional (user is creating account) (reference #405774: 'Generated password' message needed?):

Since you did not provide a password, the following was generated for you: !password

- When an admin is creating the account, the message won't show the password (for security reasons), but instead will show the following message (reference #316027: tell the password to admin, #686192: Optionally default to notify user of new account):

Since you did not provide a password, it was generated automatically for this account.

- If password was restricted (meaning, users cannot choose password on registration), then they will see the following message:

The following password was generated for you: !password

- If "Require e-mail verification when a visitor creates an account" is checked, then no password fields will appear on the regular registration form (this is Drupal's default behavior), so the module is forced into restricted mode, no matter what mode is chosen. To reflect that, I updated the description on the settings form:

Choose a password handling mode for new users. Note that if "Require e-mail verification when a visitor creates an account" is selected above, then the third option always applies for the regular user registration form. Also note that for manual user creation by an administrator, the second option always applies.

- If the password is optional, the password description is appended to say the following:

Provide a password for the new account in both fields. If left blank, a password will be generated for you.

- Another UI improvement I added is bolding the password examples on the on the user settings page, since they sometimes contain a comma, and it was hard to distinguish where the password ended.

Obviously, this is a lot, and requires some testing. I've tried all the permutations of settings I could think of, and everything looks good to me. But I'd like somebody else to check it out, too.