client: print detected path to known_host file

Use detected path instead of hard coded for error messages
core: changed type of FrameAcknowledge
core: properly set MultifragMaxRequestSize for rfx

The RemoteFX spec states that the MultifragMaxRequestSize must be at
least as big as the one received by the server. If MultifragMaxRequestSize
is too small the server disables  RemoteFX (Codec).
Merge pull request #1255 from bmiklautz/misc-fixes

Misc