Deal with implicit and duplicate constraints for variable bounds

[rschwarz]

fixes #79

Still needs additional tests. Maybe prints too many warnings now. Probably is too conservative (does not consider variable type when throwing error about existing bounds).

In particular, will still fail for these cases now:

• fixing a binary variable
• having two separate constraints, one for the lower bound, one for the upper bound

[codecov]

Codecov Report

Merging #81 into master will increase coverage by 0.63%.
The diff coverage is 93.54%.

@@            Coverage Diff            @@
##           master     #81      +/-   ##
=========================================
+ Coverage    6.42%   7.06%   +0.63%     
=========================================
  Files         121     121              
  Lines        3719    3738      +19     
=========================================
+ Hits          239     264      +25     
+ Misses       3480    3474       -6

Impacted Files	Coverage Δ
src/MOI_wrapper.jl	71.72% <93.54%> (+4.86%)	⬆️
src/wrapper/pub_var.jl	2.4% <0%> (+1.8%)	⬆️

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[coveralls]

Pull Request Test Coverage Report for Build 332

• 14 of 16 (87.5%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+2.04%) to 6.677%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/MOI_wrapper.jl	14	16	87.5%

Files with Coverage Reduction	New Missed Lines	%
src/MOI_wrapper.jl	1	67.58%

Totals
Change from base Build 329:	2.04%
Covered Lines:	249
Relevant Lines:	3729

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💛 - Coveralls

[rschwarz]

Could still add some tests (and handling) of changes in the constraint set for var bounds.