[process] Fixed asynchronous exception bugs in readProcess and readProcessWithExitCode

[Bas van Dijk]

Hi,

I fixed two asynchronous exception bugs in readProcess and
readProcessWithExitCode:

1) If an asynchronous exception was thrown to the thread executing
readProcess/readProcessWithExitCode somewhere after createProcess was
executed, the standard handles would not be closed anymore resulting
in a "handle leak" so to speak.

This is fixed by catching exceptions in the IO processing code and
closing the standard handles when an exception occurs. Additionally, I
also terminate the process and wait for its termination. Does the
latter make sense?

2) If an asynchronous exception was thrown to the
stdout/stderr-read-thread it did not execute the putMVar anymore
resulting in a dead-lock when takeMVar was executed.

This is fixed by properly catching exception in the read-thread and
propagating them to the parent thread which will then handle them as
described above.

Regards,

Bas
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