Introduce global shortcuts for x-bytes factors.

AutoTx/AutoTx.cs

@@ -29,6 +29,9 @@ namespace AutoTx
 
         private int _txProgress;
 
+        private const int MegaBytes = 1024 * 1024;
+        private const int GigaBytes = 1024 * 1024 * 1024;
+
         private DateTime _lastUserDirCheck = DateTime.Now;
 
         // the transfer state:

AutoTx/SystemChecks.cs

@@ -61,7 +61,7 @@ namespace AutoTx
         private long GetFreeDriveSpace(string drive) {
             try {
                 var dInfo = new DriveInfo(drive);
-                return dInfo.TotalFreeSpace / 1048576; // convert bytes to MB
+                return dInfo.TotalFreeSpace / MegaBytes;
             }
             catch (Exception ex) {
                 writeLog("Error in GetFreeDriveSpace(" + drive + "): " + ex.Message);