Added FD_CLOEXEC flag to client/server socket file descriptors

Added FD_CLOEXEC flag to client/server socket file descriptors

Without the FD_CLOEXEC, all subprocesses will inherit the open socket
file descriptors of the current process due to the default behavior
of fork()+exec().

Committed: https://code.google.com/p/dart/source/detail?r=14952

[kustermann, 2012-11-15 11:20:57]

PTAL

[Mads Ager (google), 2012-11-15 11:24:05]

LGTM!!!

Thanks for fixing this Martin. For extra context for people doing a drive-by,
this means that sub-processes that have not yet died cannot block the reuse of a
server socket used in the parent process.