Topology improvement around the term virtual topology

[cniethammer]

Problem

The topology chapter is not consistent in the use of 'virtual topology'

Proposal

Make consistent use of 'virtual topology'

Changes to the Text

See https://github.com/mpi-forum/mpi-standard/pull/765

Impact on Implementations

None

Impact on Users

Clarification

References and Pull Requests

https://github.com/mpi-forum/mpi-standard/pull/765

[cniethammer]

pdf version: mpi41-report.pdf

pdf version with highlighted changes: mpi-report-diff-ticket-650.pdf