Change the semantics of the "--client-speed" option such that we may add
further internal logic for other cases as well, e.g. very slow connections.
The value is now in Mbits.

* subversion/svnserve/svnserve.c
  (svnserve__options): change the wording
  (main): use new scaling factor; don't optimize the network for < 1Gb/s

Suggested by: rhuijben

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1466918 13f79535-47bb-0310-9956-ffa450edef68