Add the copyright file for flex into the tarball too.

This commit was SVN r21084.

contrib/Makefile.am

@@ -72,6 +72,7 @@ EXTRA_DIST = \
         platform/lanl/tlcc/optimized-panasas \
         platform/lanl/tlcc/optimized-panasas.conf \
         platform/win32/bin/flex.exe \
+        platform/win32/bin/COPYING.flex \
         platform/win32/opal/libltdl/ltdl.c \
         platform/win32/opal/libltdl/ltdl.h \
         platform/win32/CMakeModules/c_check_bool.cmake \