tolerate two cases of imprecision in value_set_fi; addresses issue #2653

[kroening]

No description provided.

[tautschnig]

Could a test please be added? Nit pick: will github recognise this commit message as one closing the issue?

[allredj]

This PR failed Diffblue compatibility checks (cbmc commit: fcdd39b).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/84594015
Status will be re-evaluated on next push.
Please contact @peterschrammel, @thk123, or @allredj for support.

Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)
• the author is not in the list of contributors (e.g. first-time contributors).

[allredj]

Passed Diffblue compatibility checks (cbmc commit: 3d24354).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/84596572

[NlightNFotis]

Hi @kroening, do we want to keep this? Or should this be closed?

Rebased and reviewed

[codecov]

Codecov Report

Merging #2736 (858532c) into develop (b26ad8b) will increase coverage by 0.05%.
The diff coverage is 99.10%.

@@             Coverage Diff             @@
##           develop    #2736      +/-   ##
===========================================
+ Coverage    76.76%   76.81%   +0.05%     
===========================================
  Files         1582     1582              
  Lines       182360   182771     +411     
===========================================
+ Hits        139992   140402     +410     
- Misses       42368    42369       +1     

Impacted Files	Coverage Δ
src/pointer-analysis/value_set_fi.cpp	69.51% <66.66%> (-0.07%)	⬇️
src/pointer-analysis/value_set.cpp	83.33% <100.00%> (+0.04%)	⬆️
...solvers/smt2_incremental/smt_bit_vector_theory.cpp	100.00% <100.00%> (ø)
...solvers/smt2_incremental/smt_bit_vector_theory.cpp	100.00% <100.00%> (ø)

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