fix pivoting bug of simplexMethodPD
remove unnecessary fabs() invocations.

It seems those fabs() are unnecessary: fabs(T[q][n+m]-t), fabs(T[j][n+m]-t), fabs(T[m][p]-t), fabs(T[m][i]-t).
By definition t must be smaller than all of T[q][n+m], T[j][n+m], T[m][p] and T[m][i], hence the arguments of the fabs() invocations are always positive.
Merge pull request #1 from msakai/SimplexMethodLP-fix-pivot-bug

fix pivoting bug of simplexMethodPD
Merge pull request #2 from msakai/SimplexMethodLP-remove-fabs

remove unnecessary fabs() invocations.
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