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.