20110312
  xpress.c, README.1st, README.xpress:  update to version 7.1.

20110325
  xpress.c: omit the "debug" keyword unless compiled with -DRWA_DEBUG .

20110419
  xpress.c: fix a bug with quadratic constraints involving some
variables that only appear linearly.

20110825
  xpress.c: some bug fixes, e.g., in handling quadratic forms,
supplied by David Nielsen.

20110913
  xpress.c: add support for indicator constraints, i.e., logical
constraints of the form
	s.t. foo: b == c ==> constraint1 [else constraint2]
with b a binary variable, c = 0 or 1, and the constraints simple
inequality or equality constraints.  This requires linking with
version >= 20110913 of the AMPL/solver interface library.

20111010
 xpress.c: fix a bug in the update of 20110825.

20111220
 xpress.c: increase constraint.sstatus array length by one to fix
a possible fault.

20111223
 xpress.c: catch SIGINT (control-C) and return the best available
solution.  Quickly giving several control-C's may sometimes lead to
the new solve_result_num value 520 (and no returned solution).
 README.xpress: minor adjustments.

20120417
 xpress.c: updates for XPRESS 22.