Fixing a bunch of format strings.

Also leveraging GCC if available to check format specificier.

Closes #567.

src/Reporter.h

@@ -15,6 +15,13 @@
 class Connection;
 class Location;
 
+// Check printf-style variadic arguments if we can.
+#if __GNUC__
+#define FMT_ATTR __attribute__((format(printf, 2, 3))) // sic! 1st is "this" I guess.
+#else
+#define FMT_ATTR
+#endif
+
 class Reporter {
 public:
 	Reporter();
@@ -22,25 +29,25 @@ public:
 
 	// Report an informational message, nothing that needs specific
 	// attention.
-	void Info(const char* fmt, ...);
+	void Info(const char* fmt, ...) FMT_ATTR;
 
 	// Report a warning that may indicate a problem.
-	void Warning(const char* fmt, ...);
+	void Warning(const char* fmt, ...) FMT_ATTR;
 
 	// Report a non-fatal error. Processing proceeds normally after the error
 	// has been reported.
-	void Error(const char* fmt, ...);
+	void Error(const char* fmt, ...) FMT_ATTR;
 
 	// Returns the number of errors reported so far.
 	int Errors()	{ return errors; }
 
 	// Report a fatal error. Bro will terminate after the message has been
 	// reported.
-	void FatalError(const char* fmt, ...);
+	void FatalError(const char* fmt, ...) FMT_ATTR;
 
 	// Report a fatal error. Bro will terminate after the message has been
 	// reported and always generate a core dump.
-	void FatalErrorWithCore(const char* fmt, ...);
+	void FatalErrorWithCore(const char* fmt, ...) FMT_ATTR;
 
 	// Report a traffic weirdness, i.e., an unexpected protocol situation
 	// that may lead to incorrectly processing a connnection.
@@ -51,15 +58,15 @@ public:
 
 	// Syslog a message. This methods does nothing if we're running
 	// offline from a trace.
-	void Syslog(const char* fmt, ...);
+	void Syslog(const char* fmt, ...) FMT_ATTR;
 
 	// Report about a potential internal problem. Bro will continue
 	// normally.
-	void InternalWarning(const char* fmt, ...);
+	void InternalWarning(const char* fmt, ...) FMT_ATTR;
 
 	// Report an internal program error. Bro will terminate with a core
 	// dump after the message has been reported.
-	void InternalError(const char* fmt, ...);
+	void InternalError(const char* fmt, ...) FMT_ATTR;
 
 	// Toggle whether non-fatal messages should be reported through the
 	// scripting layer rather on standard output. Fatal errors are always