New table Log::rotation_control that enables to control rotation

for individual files, overriding defaults.

The interface isn't the greatest but the best I can come up with right
now.

src/LogMgr.h

@@ -99,6 +99,7 @@ private:
 	void RemoveDisabledWriters(Stream* stream);
 	void InstallRotationTimer(WriterInfo* winfo);
 	void Rotate(WriterInfo* info);
+	RecordVal* LookupRotationControl(EnumVal* writer, string path);
 
 	vector<Stream *> streams; // Indexed by stream enum.
 };