pan2 did not install on SnowLeopard and Xode 4

[Ryan Schmidt]

On Sep 5, 2015, at 8:51 AM, David Evans wrote:

> However, it does build and run with libstdc++ using
> 
> configure.cxx_stdlib libstdc++
> 
> because none of its dependencies use libc++.
> 
> Since it's not likely that any other port using libc++ will have a binary dependency on pan2, isn't this a permissible
> configuration for this port on Mavericks and Yosemite until the libc++ issue is addressed upstream? Haven't checked
> whether this will work on El Capitan as yet.

Great idea. Committed just this change.