Fix NickServ ACC command short descrption

All command short descriptions returned by `/msg NickServ HELP COMMANDS` end with a period except for the ACC command. This pull request simply fixes a grammatical inconsistency in the project.
protocol/unreal: fix checking of +f syntax

check_flood would immediately return false regardless of action char
validity, and check_flood_old was expecting a ':' but actually checked
for '*'.
nickserv/{enforce,ghost}: respect frozen accounts

This further avoids allowing access of frozen accounts, most critically
in the case of the NickServ REGAIN command which would otherwise allow
logging in to a frozen account.