Make `cleanupProcess` resistant to SIGPIPE

Otherwise, `cleanupProcess` may exit prematurely if trying to flush out
data to the process' stdin handle even though the endpoint has already
vanished, and fail to complete the cleanup process.

See also 228297ec53e9ee7a1a6a3c5964ca7e89a6474c9b and #2233.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Add Haddock note to `call{Command,Process}` wrt execptions (#2233)

This also tweaks Haddock comments & markup in "System.Process" while at it.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Minor update to changelog file

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>