introducing the disk formats for _RuneLocale and friends.
The disk formats do not have (useless) pointers and have 32-bit
quantities instead of rune_t and long. (htonl(3) only works
with 32-bit quantities, so there's no loss).
Bootstrap mklocale(1) when necessary. (Bootstrapping from 4.x
would be trivial (verified), but we no longer provide pre-5.3
source upgrades and this is the first commit to actually break
it.)
