*  start=4000
logic to determine ntape,mtape
ntape=1  data read from iobcon overrides that read from iobs,iabs1
(whether iobs,iabs1 are read depends on mtape)
ntape=2  data read from iobs overrides that read from iabs1  (iobcon
is not read, whether iabs1 is read depends on mtape)
ntape=3  data read from iabs1, but not from iobcon,iobs
mtape=-1 dummy observations generated from iobcon (ntape must be 1)
mtape=0  data read from both iobs and iabs1 (ntape can be 1 or 2)
mtape=1  data read from iobs, not from iabs1 (ntape can be 1 or 2)
mtape=2  data read from iabs1, not from iobs (ntape can be 1 or 3)
niobc,niobs,and/or niabs1 are set to zero if mtape,ntape indicate
that iobcon,iobs and/or iabs1, respectively, are to be read beyond
first record of observation series

all series on a single obslib tape have, by definition,
the same value of ntape.  thus, unlesss ict(80) is
negative (no input obslib) or the series is a dummy
(already checked), a jump in ntape from iobs should
force a new output tape.

determine tape numbers:
iiobcn,iiobs,iiabs1 are iobcon,iobs,iabs1 or 0
according to whether they are read or not
set ntape,mtape from jobf

calculate lx vectors for parameters affecting every observ.
use of 'life' for status of iabs2
-2 - checkpoint restart just begun
-1 - nothing done yet
0 - l-vectors merged for header (if needed)
1 - header written