add support for qscan renumbering into wwivutil fix

[wwiv]

WWIV 4.x FIX had a function void find_max_qscan(void) which would renumber the qscan of all messages. Seems like a good thing to add. Mark can use it then.

[wwiv]

Here's a doc with the proposal: https://docs.google.com/document/d/1pA-DRuhdweN4x4KvAqlwmAojo9jjmegebYLSYbJ7ImY/edit?usp=gmail

[wwiv]

Memory Requirements:

For each cell in the map, need 8 bytes (4 bytes * 2) Say 1k users and 1k subs, that's 1m * 8 == 8m ram needed.

Each sub can be read in ram at one time.
Say 100k messages, 100 bytes/header = 10m.

Total needed high water mark = 18m

# Algorithm:

Qo = Original QScan Pointer
Qn = New QScan Pointer
Create Map ( Qo -> Qn )

### Create the list of interesting qscan values
For each user U:
  For each area A:
     Put map ( user.qsc_p[A] -> 0 )

### Renumber message area
Let Qn = 0
For each area:
  For each message m:
    If map contains (m.qscan):
      // Update mapping of old to new qscan pointer
      map put(m.qscan, Qn)
    Let m.qscan = Qn;
    Qn ++

### Now map(Qo -> Qn) is complete.
### Renumber the qscan pointers
For each user U:
  For each area A:
    let oq = user.qsc_[A]
    let nq = map.lower_bound(oq);
    if nq is found:
      set user.qsc[A] =  nq.value
    else:
      # Set to highest possible value.
      set user.qsc[A] = Qn