Workaround for running DTH on mono

The process Exited event fires even though the caller is still running.
This is a workaround that skips the event altogether. This does mean
however that the caller will be responsible for terminating DTH on
mono environments.
Merge pull request #873 from OmniSharp/dev

Workaround for running DTH on mono
Give a warning in the KRE trace log when PDB generation is not supported
Copy the minimal set of dlls required for the KRE/kpm and DTH to run
Removed useless variable