filter out failed exec calls

[rizsotto]

This requires post processing or delayed writes. The information about the exec fails is available only when the exec returns with an error code. It means the client lib shall connect twice. (And maybe the between the two connections there were another client wrote something.)

Plan to change the protocol between the client lib and the bin...

MSG { pid, method, args, cwd }
MSG { pid, result }

Client code would write all of them into a file and do post processing when child process quits.

[rizsotto]

debug output does contain the first message attributes { pid, ppid, method, args, cwd }

[rizsotto]

Might be not as useful. Postponed to later.

[rizsotto]

maybe filtering not, but reporting might be interesting (in debug mode)

[breser]

This would be helpful on OS X where the implementation of the exec functions that support PATH loop over calls to execve() until it works, which results in duplicate entries until it finds the correct path.