Find ssh commands via locate

[uenz]

SparkleShare uses several comandline tools to provide functionality. While working on the windows version i saw that ssh, ssh-keygen and ssh-keyscan was hard coded and sparkleshare expects that these are in the path. This is not always given. I extended the SSHCommand.cs to da the location of all ssh related commands. The additional calls in BaseController.cs checks for existance of the shs commands. As ssh-keyscan and ssh-keygen does not provide a version info they are called to check if they are there. The enquating is changed from ' to ", because this is the platform independent way.