turning ExitCode into an IO exception

[Henning Thielemann]

Is there a prefered way to convert an ExitCode to an IO exception? When 
running a sequence of IO actions, it is certainly best to use the same way 
of showing failure for all of them. However running shell commands with 
functions from the 'process' package shows failure by ExitCode which is 
different from almost all other IO actions in 'base'.