A better long term fix for stopping the process when it is running by writing...

A better long term fix for stopping the process when it is running by writing to the pipe that was used for cancel. 

We now write a 'q' to indicate to exit the IOHandlerProcessSTDIO::Run(), and a 'i' to interrupt the process. This should make this code safer to use in a signal handler function.

llvm-svn: 202311