move log/debug codebase to libosmocore

The logging/debugging code is generic enough to move it into libosmocore
while keeping OpenBSC specific definitions in openbsc itself.

This commit uses the logging support present in libosmocore-0.1.2,
you will have to update your library to this version.
diff --git a/openbsc/src/abis_rsl.c b/openbsc/src/abis_rsl.c
index 0c3b597..3e0c014 100644
--- a/openbsc/src/abis_rsl.c
+++ b/openbsc/src/abis_rsl.c
@@ -118,8 +118,8 @@
 	}
 
 	lchan = &ts->lchan[lch_idx];
-	debug_set_context(BSC_CTX_LCHAN, lchan);
-	debug_set_context(BSC_CTX_SUBSCR, lchan->conn.subscr);
+	log_set_context(BSC_CTX_LCHAN, lchan);
+	log_set_context(BSC_CTX_SUBSCR, lchan->conn.subscr);
 
 	return lchan;
 }