passes stdin from CompileDaemon to the built command

[pigfrown]

This PR allows user to pass input to the launched command via stdin.

It gets a stdinPipe from the launched command and returns it from startCommand. Two goroutines are launched, one to write stdin to a channel, another to read that channel and write the contents to the launched command's stdinPipe.

Previous pull request closed as it didn't work correctly when a command was relaunched.