20091104
  gurobi.c, README.gurobi: fix a glitch with iisfind=1 on infeasible
problems:  solve_result_num previously indicated a failure rather
than infeasible.

20091214
  gurobi.c: add "cutoff" keyword to possibilities for $gurobi_options.
  makefile.u: add rule for xsum.out.
  README.gurobi: add brief MacOSX discussion.

20100309
  gurobi.c: fix bugs in handling .ref and .sosno suffixes.

20100418
  gurobi.c:  extend for Gubobi 3.0; should continue to work with older
versions of Gurobi as well.  New facilities include keywords for
requesting .sol files of alternative MIP solutions; new synonym
lpmethod for simplex and a way to select the (new) barrier algorithm
(lpmethod=2); new tolerances and an iteration limit for the barrier
method; control of crossover from barrier solution to basic solution;
"mipfocus" to help direct the MIP solver; "predual" to present the
dual of an LP to the solver; "pumppasses" to control the feasibility
pump; and "symmetry" to control the MIP solver's detection of
symmetry.  See the output of "gurobi -=" for a summary of the
currently available keywords.  Complete list of new keywords for
Gurobi 3.0:  aggfill, ams_eps, ams_epsabs, ams_limit, ams_stub,
barconvtol, barcorrectors, bariterlim, barorder, crossover,
crossoverbasis, lpmethod, mipfocus, mipgapabs, networkcuts, param,
paramfile, predeprow, predual, prepases, pumppasses, resultfile,
rins, submipcuts, symmetry.

20100424
  gurobi.c:  fix a couple of typos in the "-=" output; correct
spelling of "prepasses" and for now make "prepases" a deprecated
synonym for "prepasses".

20100512
  gurobi.c: adjust for a gratuitous parameter name change
("LogfileName" to "LogFile") between versions 2 and 3.

20100523
  gurobi.c: adding keyword return_mipgap for returning suffixes
absmipgap and relmipgap on objectives and problems.  (These values
could already be computed from the bestbound suffix.)

20100720
  gurobi.c: distinguish explicitly zero initial guesses from those
that are zero by default.  This affects MIP starting guesses.

20100928
  gurobi.c: expand description of sos2 (shown with "gurobi -=").

20101021
   gurobi.c: fix some bugs in statmsg() with error messages not
normally seen.

20101105
  gurobi.c, README.gurobi: update for Gurobi 4.0.

20101115
  gurobi.c:  fix a bug (introduced in adjustments for Gurobi 4) that
sometimes caused the constant term in objectives to be treated as 0.
This affected the objective value reported.

20101207
  gurobi.c, README.gurobi:  set solve_result_num = 567 if the problem has
complementarity constraints.

20110322
  gurobi.c: fix a bug in handling problems with integer variables
(including binary variables) and piecewise-linear terms:  the wrong
variables were likely treated as integer.  Fix a bug with "writeprob"
that could occur in problems with piecewise-linear terms:  a call on
GRBupdatemodel() was missing, which could affect, e.g., a *.lp file
specified by writeprob.

20110426
  gurobi.c, README.gurobi: update to Gurobi 4.5.  The updated gurobi.c
should still work with earlier versions.  The new .unbdd and .dunbdd
suffixes (for primal and dual rays of unboundedness) are not yet
reliable.

20110728
  gurobi.c:  fix a glitch with sos=1 in $gurobi_options that prevented
.sosno and .ref from being used in problems with only continuous
variables.

20110920
  gurobi.c:  add "method"; move the "lpmethod" description to "method"
and list lpmethod as a synonym for method.  (Driver date 20110907.)
  README.gurobi, makefile.*: minor tweaks for less dependence on the
particular version of Gurobi.

??
  gurobi.c: fix a minor glitch in reporting the names of alternate
solution files generated when ams_stub is specified in $gurobi_options.
Update for use with Gurobi 4.6; new keywords:
	presparsify
	priorities
	sifting
	siftmethod
	zeroobjnodes
The priorities keyword controls whether variable.priority values, if
available, are passed to Gurobi.  (Default = yes.)

20111109
  gurobi.c:  update for Gurobi 4.6.  Should still work with earlier
versions of Gurobi.

20120504
  gurobi.c, README.gurobi, makefile.u: update for Gurobi 5.0.  The
updated gurobi.c should still work with earlier versions of Gurobi.

20120511
  gurobi.c: fix a bug (fault) in supplying a warm start.

20120524
  gurobi.c: fix a typo in the "gurobi -=" output.