import gprs_gsup_message.[ch] from openbsc as gsup.[ch]

Move those routines from OpenBSC to libosmogsm, so they can be
re-used from other programs.  I think it was a mistake to add them only
inside the openbsc repository in the first place.  We need to pay more
attention to this in the future.
diff --git a/tests/gsup/gsup_test.ok b/tests/gsup/gsup_test.ok
new file mode 100644
index 0000000..1285897
--- /dev/null
+++ b/tests/gsup/gsup_test.ok
@@ -0,0 +1,14 @@
+Test GSUP message decoding/encoding
+  Testing Send Authentication Info Request
+  Testing Send Authentication Info Error
+  Testing Send Authentication Info Result
+  Testing Update Location Request
+  Testing Update Location Error
+  Testing Update Location Result
+  Testing Location Cancellation Request
+  Testing Location Cancellation Error
+  Testing Location Cancellation Result
+  Testing Purge MS Request
+  Testing Purge MS Error
+  Testing Purge MS Result
+Done.