TST: test 2x2 and 3x3 determinants using explicit formulas
bugfix in test_logdet: input should have positive determinant
Merge remote-tracking branch 'alex/more-det-testing'
TST: test the identity trace(x) == logdet(expm(x))
TST: require a positive semidefinite matrix for the trace/logdet/expm test
Merge pull request #44 from argriffing/more-det-testing

TST: test 2x2 and 3x3 determinants using explicit formulas