fixing the comparisons with infinity

[lipchev]

• added extra tests for the CompareTo and the Equals methods
• updated the benchmark results (no difference w.r.t. ref readonly modifier)

[lipchev]

@danm-de I cannot reopen the previous PR so here is another one. There are perhaps way too many tests but I've been using them to test every return statement on my optimized implementation. It's almost ready, and significantly faster- but I want to check a few more things before I publish it (probably tonight), so it would be easier if kept the extra tests for now..