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
Merge pull request #184 from jucor/assert_error

Add new asserts to Tester