WL#3870: New Falcon@@ settings

Three new settings are being added to the server @@ variables, now that worklog
1722 is done and they can be done without changing the server code.  These
settings already exist in the Falcon engine and are now being exposed.  They can
be set at any time, but are only applied to Falcon the first time a Falcon table
is accessed.

Name:        falcon_log_windows
Description: The number of memory windows allocated for Falcon serial log.
Minimum:     10
Maximum:     32768
Default:     10

Background:  Each of these windows are 1 Mbyte in size, so you don't want to
have more than you really need.  When these are all used by concurrent threads,
however, things will start to back up.  At present, this number of serial log
windows is allocated for each serial log.  But in the future, this will be a
maximum number of windows, and Falcon will allocate only what it needs for
concurrent threads, but not more than this number.

Name:        falcon_index_chill_threshold
Description: Mbytes of pending index data that is 'frozen' to the 
             Falcon serial log..
Minimum:     1
Maximum:     1024
Default:     4

Background:  This is the number of Mbytes of pending index data that Falcon will
store during a large transaction before flushing these index changes to the
serial log.  This 'flushing' is called 'chilling' the index since it makes the
data not immediately available.  If the index is unique, or the transaction
regularly re-reads this index data, it stays in memory.  Chilling pending
indexes helps Falcon to accomplish very large data loads in a single transaction
without running out of memory. See Worklog 3714.

Name:        falcon_record_chill_threshold
Description: Mbytes of pending record data that is 'frozen' to the 
             Falcon serial log.
Minimum:     1
Maximum:     1024
Default:     5

Background:  This is the number of Mbytes of pending record data that Falcon
will keep in memory during a large transaction before flushing these records to
the serial log.  This 'flushing' is called 'chilling' since it makes the data
not immediately available.  If chilled records are accessed again during the
transaction, they are immediately restored (thawed) from the serial log. 
Chilling pending records helps Falcon to accomplish very large transactions
without running out of memory. See Worklog 3722.