library: Initial work on GPRS RLC/MAC encoder/decoder

For Downlink and Uplink RLC/MAC Control blocks this is already working
quite nicely.  Data blocks is not working, as their encoding cannot be
expressed in TTCN-3 RAW syntax, and a mixture of C++/native and
RAW-generated coder will be required.
diff --git a/library/GSM_SystemInformation.ttcn b/library/GSM_SystemInformation.ttcn
index 74852d4..90fa425 100644
--- a/library/GSM_SystemInformation.ttcn
+++ b/library/GSM_SystemInformation.ttcn
@@ -15,7 +15,7 @@
 	} with { variant "" };
 
 	/* 24.008 10.5.1.1 */
-	type uint16_t CellIdentity;
+	type uint16_t SysinfoCellIdentity;
 
 	/* 44.018 10.5.2.1b */
 	type octetstring CellChannelDescription with { variant "FIELDLENGTH(16)" };
@@ -117,7 +117,7 @@
 
 	/* 44.018 9.1.35 */
 	type record SystemInformationType3 {
-		CellIdentity			cell_id,
+		SysinfoCellIdentity		cell_id,
 		LocationAreaIdentification	lai,
 		ControlChannelDescription	ctrl_chan_desc,
 		CellOptions			cell_options,
@@ -164,7 +164,7 @@
 
 	/* 44.018 9.1.40 */
 	type record SystemInformationType6 {
-		CellIdentity			cell_id,
+		SysinfoCellIdentity		cell_id,
 		LocationAreaIdentification	lai,
 		CellOptionsSacch		cell_options,
 		BIT8				ncc_permitted,