[Xastir] Xastir on Mac OS X with Homebrew for dependencies

[Tom Russo]

Inspired by a question on the Facebook APRS page, I went ahead today and
installed Xastir from source on a Mac laptop by using homebrew (https://brew.sh)
as the package manager for all the dependent libraries.  It went off with 
hardly a hitch (the only hitch being that you have to do something special
to get homebrew to use Berkeley DB 4.x instead of 6.x, and Xastir is not
yet set up to build with 6.x).

I documented the process on the Xastir Wiki by adding a new installation note.

-- 
Tom Russo    KM5VY
Tijeras, NM  

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