Extend assertError and fix global

Two new asserts: assertErrorMsg and assertErroObj,
to compare the actual error message or object returned.
Add assertErrorPattern
Make error message clearer
Add Tester:assertalmosteq()
Display error returned if not the expected one
Test for new asserts
Remove my now-obsolete TODO in assertTableEq
Fix typo in assertalmosteq
Plot time for constant array
Fix quicksort for constant arrays

Change the comparison with the pivot to strict inequality, not or-equal.
This solves the terrible performance of sorting a constant array.
Add bibliographic reference
Add tests for sorting with equal keys
Fix bug in potrf wrapping: return a triangular matrix

The cholesky decomposition is supposed to be upper triangular.
The wrapper for Lapack's `potrf`, instead, filled the resulting matrix to make
it symmetric. Since this behaviour was introduced in commit 971973d0, which
dealt with C89 and added such lines for several wrappers, I wonder if
this was not a copy/paste overlook.

This patch also adds a test for the cholesky decomposition.
Test that Cholesky errs on rank-deficient input
Merge pull request #188 from jucor/TriangularCholesky

Fix possible bug in potrf wrapping: return a triangular matrix
Merge pull request #184 from jucor/assert_error

Add new asserts to Tester
Merge pull request #185 from jucor/lazy_faster

Fix quicksort on constant arrays