Support sending and receiving account timestamps (but ignore them for now).

Support sending and receiving account timestamps (but ignore them for now).

src/hash.h (account_func_t): Add timestamp and serial ID fields.
  (call_account_func): Likewise.
  (StampUser): Likewise.
src/hash.c (call_account_func): Pass them through to account_func.
  (StampUser): Pass them through to irc_account.
src/nickserv.h (handle_info::id): Make this field unconditional.
src/nickserv.c (register_handle): Make the ID assignment unconditional.
  (free_handle_info): Make the ID handling here unconditional.
  (set_user_handle_info): Pass all the ID fields to StampUser().
  (cmd_handleinfo): Move NSMSG_HANDLEINFO_ID to be staff only.
  (nickserv_saxdb_write): Make the ID assertion and write unconditional.
  (nickserv_db_read_handle): Remove redundant "int".
  (handle_account): Use account name preferentially, fall back to ID.
src/proto.h (irc_account): Add timestamp and serial number parameters.
src/proto-bahamut.c (AddUser): Make stamp parameter unsigned long.  Pass
    it appropriately to call_account_func().
  (irc_account): Add timestamp and serial number parameters; use serial
    number in place of a base64-decoded stamp.
src/proto-p10.c (irc_account): Send timestamp and serial number for user.
  (cmd_account): Parse them when they are present.
  (mod_usermode): Likewise.