#117 Compile on cygwin

[Ian Sheldon]

Cygwin doesn't provide either MSG_DONTWAIT or
AF_INET6. Minor patch to conditionally check for this.
The only alternative cygwin has is to use the default flag
instead of MSG_DONTWAIT, which shouldn't be a
problem for udp.

Maybe the checks should be moved to the configure
script?

This makes the code work under cygwin on XP.
Unfortunately XP SP2 limits the number of pending
socket connects so many of the config limits need to be
reduced to use it (e.g., connection pool size, number
concurrent downloads).

Hope it's useful.

[Ian Sheldon]

patch to enable compilation under cygwin

[Christian Biere]

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Thanks, I've modified the sources so that these two are not
in your way anymore.