Fixed mathematically wrong statement in the documentation of scala.math.PartialOrdering.
Fixed mathematically wrong statement in the documentation of scala.math.PartialOrdering.

- Previous (misleading) documentation suggested that a partial ordering *is* an equivalence relation. This has now been clarified.
- Existing documentation on properties of partial orderings (reflexive, transitive, antisymmetric) had several formatting inconsistencies that have now been remove.

felixmulder/scala,slothspot/scala,shimib/scala,lrytz/scala,lrytz/scala,martijnhoekstra/scala,felixmulder/scala,slothspot/scala,scala/scala,slothspot/scala,jvican/scala,slothspot/scala,scala/scala,slothspot/scala,scala/scala,martijnhoekstra/scala,lrytz/scala,martijnhoekstra/scala,scala/scala,jvican/scala,felixmulder/scala,jvican/scala,felixmulder/scala,felixmulder/scala,lrytz/scala,felixmulder/scala,martijnhoekstra/scala,scala/scala,shimib/scala,lrytz/scala,martijnhoekstra/scala,jvican/scala,shimib/scala,slothspot/scala,shimib/scala,jvican/scala,lrytz/scala,jvican/scala,slothspot/scala,martijnhoekstra/scala,shimib/scala,felixmulder/scala,scala/scala,jvican/scala,shimib/scala