Add AUTHORS file for X11 from xlibs tree.

AUTHORS

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+The architect of the X11 core protocol was Bob Scheifler of MIT LCS, with
+significant contributions from Jim Gettys, Phil Karlton and Scott
+McGregor of Digital, Dave Rosenthal of Sun, and many others of
+the xpert mailing list.
+
+The original sample server implementation of the X11 protocol was
+implemented by Phil Karlton and Susan Angebrandt doing the device
+independent part of the server, with Raymond Drewry and Todd Newman of
+Digital Equipment Corporation, doing the mi and original ddx
+implementation; their feedback was vital to a good design, along with
+that of the more than 100 alpha and beta testers who bravely tested
+the X11 core design.
+
+The X11 protocol library (Xlib) was built principally by Jim Gettys of
+Digital and MIT Project Athena, with assistance from Ron Newman of MIT
+Project Athena.
+
+Our thanks to those at MIT, Digital Equipment Corporation, Hewlett-Packard,
+IBM, and many others who had faith in us reimplementing X from first
+principles.
+
+If there are mistakes here, they are mine; entirely possible after
+over 15 years. - Jim Gettys