use double underscores in the MAGIC identifiers

these magic constants aren't intended for use by client code. add a
double underscore to indicate this.

protobuf-c/protobuf-c.c

@@ -75,16 +75,16 @@
 /* Assertions for magic numbers. */
 
 #define ASSERT_IS_ENUM_DESCRIPTOR(desc) \
-	assert((desc)->magic == PROTOBUF_C_ENUM_DESCRIPTOR_MAGIC)
+	assert((desc)->magic == PROTOBUF_C__ENUM_DESCRIPTOR_MAGIC)
 
 #define ASSERT_IS_MESSAGE_DESCRIPTOR(desc) \
-	assert((desc)->magic == PROTOBUF_C_MESSAGE_DESCRIPTOR_MAGIC)
+	assert((desc)->magic == PROTOBUF_C__MESSAGE_DESCRIPTOR_MAGIC)
 
 #define ASSERT_IS_MESSAGE(message) \
 	ASSERT_IS_MESSAGE_DESCRIPTOR((message)->descriptor)
 
 #define ASSERT_IS_SERVICE_DESCRIPTOR(desc) \
-	assert((desc)->magic == PROTOBUF_C_SERVICE_DESCRIPTOR_MAGIC)
+	assert((desc)->magic == PROTOBUF_C__SERVICE_DESCRIPTOR_MAGIC)
 
 /* --- version --- */
 
@@ -2661,7 +2661,7 @@ protobuf_c_message_check(const ProtobufCMessage *message)
 {
 	if (!message ||
 	    !message->descriptor ||
-	    message->descriptor->magic != PROTOBUF_C_MESSAGE_DESCRIPTOR_MAGIC)
+	    message->descriptor->magic != PROTOBUF_C__MESSAGE_DESCRIPTOR_MAGIC)
 	{
 		return FALSE;
 	}

protobuf-c/protobuf-c.h

@@ -505,9 +505,9 @@ do {									\
 
 /* ====== private ====== */
 
-#define PROTOBUF_C_SERVICE_DESCRIPTOR_MAGIC	0x14159bc3
-#define PROTOBUF_C_MESSAGE_DESCRIPTOR_MAGIC	0x28aaeef9
-#define PROTOBUF_C_ENUM_DESCRIPTOR_MAGIC	0x114315af
+#define PROTOBUF_C__SERVICE_DESCRIPTOR_MAGIC	0x14159bc3
+#define PROTOBUF_C__MESSAGE_DESCRIPTOR_MAGIC	0x28aaeef9
+#define PROTOBUF_C__ENUM_DESCRIPTOR_MAGIC	0x114315af
 
 /*
  * A little enum helper macro: this will ensure that your enum's size is

protoc-c/c_enum.cc

@@ -272,7 +272,7 @@ void EnumGenerator::GenerateEnumDescriptor(io::Printer* printer) {
   printer->Print(vars,
     "const ProtobufCEnumDescriptor $lcclassname$__descriptor =\n"
     "{\n"
-    "  PROTOBUF_C_ENUM_DESCRIPTOR_MAGIC,\n"
+    "  PROTOBUF_C__ENUM_DESCRIPTOR_MAGIC,\n"
     "  \"$fullname$\",\n"
     "  \"$shortname$\",\n"
     "  \"$cname$\",\n"

protoc-c/c_message.cc

@@ -467,7 +467,7 @@ GenerateMessageDescriptor(io::Printer* printer) {
   printer->Print(vars,
   "const ProtobufCMessageDescriptor $lcclassname$__descriptor =\n"
   "{\n"
-  "  PROTOBUF_C_MESSAGE_DESCRIPTOR_MAGIC,\n"
+  "  PROTOBUF_C__MESSAGE_DESCRIPTOR_MAGIC,\n"
   "  \"$fullname$\",\n"
   "  \"$shortname$\",\n"
   "  \"$classname$\",\n"

protoc-c/c_service.cc

@@ -226,7 +226,7 @@ void ServiceGenerator::GenerateServiceDescriptor(io::Printer* printer)
 
   printer->Print(vars_, "const ProtobufCServiceDescriptor $lcfullname$__descriptor =\n"
                        "{\n"
-		       "  PROTOBUF_C_SERVICE_DESCRIPTOR_MAGIC,\n"
+		       "  PROTOBUF_C__SERVICE_DESCRIPTOR_MAGIC,\n"
 		       "  \"$fullname$\",\n"
 		       "  \"$name$\",\n"
 		       "  \"$cname$\",\n"