Redesign automatic supply interface

Redesign automatic supply interface

The automatic supply interface has design flaws that make it hard to
use correctly.  Its current uses are in fact all wrong (until commit
0179fd86, the update had a few uses that might have been correct).
Some of the bugs can only bite with land unit capability combinations
that don't exist in the stock game, though.

Automatic supply draws supplies from supply sources in range.  Since
that can update any supply source in range, all copies of potential
supply sources a caller may keep can get invalidated.  Writing back
such an invalid copy wipes out the deduction of supplies and mobility
from a source, triggering a seqno mismatch oops.

This commit redesigns the interface so that callers can safely keep a
copy of the object drawing the supplies (the "supply sink").  The idea
is to pass the sink to the supply code, so it can avoid using it as
source.  The actual avoiding will be implemented in a later commit.

Copies other than the supply sink still need to be eliminated.  See
commit 65410d16 for an example.

Other improvements to help avoid common errors:

* Supply functions are commonly used to ensure the sink has a certain
  amount of supplies.  A common error is to fetch that amount
  regardless of how many the sink already has.  It's more convenient
  for such users to pass how many they need to have instead of how
  many to get.

* A common use of supply functions is to get supplies for immediate
  use.  If that use turns out not to be possible after all, the
  supplies need to be added somewhere, which is all too easy to
  forget.  Many bugs of this kind have been fixed over time, and there
  are still some left.  This class of bugs can be avoided by adding
  the supplies to the sink automatically.

In fact, this commit fixes precisely such bugs in mission_pln_equip()
and shp_missile_defense(): plane interception and support missions,
missile interception (abms), launch of ballistic missiles and
anti-sats could all lose shells, or supply more than needed.

Replace supply_commod() by new sct_supply(), shp_supply(),
lnd_supply(), and resupply_all() by new lnd_supply_all().  Simplify
users accordingly.

There's just one use of resupply_commod() left, in landmine().  Use
lnd_supply_all() there, and remove resupply_commod().