Use global variables for incoming and managed paths.

This avoids building them over and over again with Path.Combine() which
is not necessary as they are static anyway and won't change after the
configuration has been parsed and verified.

References issue #7.

AutoTx/AutoTx.cs

@@ -19,6 +19,8 @@ namespace AutoTx
         // ending with "Dir" are DirectoryInfo objects
         private string _configPath;
         private string _statusPath;
+        private string _incomingPath;
+        private string _managedPath;
         private List<string> _transferredFiles = new List<string>();
 
         private int _txProgress;
@@ -142,14 +144,18 @@ namespace AutoTx
                              @" and a backslash, e.g. 'D:\'!");
                     configInvalid = true;
                 }
+                // IncomingDirectory
                 if (_config.IncomingDirectory.StartsWith(@"\")) {
                     writeLog("ERROR: IncomingDirectory must not start with a backslash!");
                     configInvalid = true;
                 }
+                _incomingPath = Path.Combine(_config.SourceDrive, _config.IncomingDirectory);
+                // ManagedDirectory
                 if (_config.ManagedDirectory.StartsWith(@"\")) {
                     writeLog("ERROR: ManagedDirectory must not start with a backslash!");
                     configInvalid = true;
                 }
+                _managedPath = Path.Combine(_config.SourceDrive, _config.ManagedDirectory);
                 if (_config.ServiceTimer < 1000) {
                     writeLog("ERROR: ServiceTimer must not be smaller than 1000 ms!");
                     configInvalid = true;
@@ -535,8 +541,7 @@ namespace AutoTx
                 return;
 
             // select next directory from "processing" for transfer:
-            var processingDir = Path.Combine(_config.SourceDrive,
-                _config.ManagedDirectory, "PROCESSING");
+            var processingDir = Path.Combine(_managedPath, "PROCESSING");
             var queued = new DirectoryInfo(processingDir).GetDirectories();
             if (queued.Length == 0)
                 return;
@@ -555,9 +560,8 @@ namespace AutoTx
         /// Check the incoming directories for files, move them to the processing location.
         /// </summary>
         private void CheckIncomingDirectories() {
-            var incomingPath = Path.Combine(_config.SourceDrive, _config.IncomingDirectory);
             // iterate over all user-subdirectories:
-            foreach (var userDir in new DirectoryInfo(incomingPath).GetDirectories()) {
+            foreach (var userDir in new DirectoryInfo(_incomingPath).GetDirectories()) {
                 if (IncomingDirIsEmpty(userDir))
                     continue;
 
@@ -704,8 +708,8 @@ namespace AutoTx
                 
                 // now everything that is supposed to be transferred is in a folder,
                 // for example: D:\ATX\PROCESSING\2017-04-02__12-34-56\user00
-                var targetDir = Path.Combine(_config.SourceDrive,
-                    _config.ManagedDirectory,
+                var targetDir = Path.Combine(
+                    _managedPath,
                     target,
                     CreateTimestamp(),
                     userDir.Name);
@@ -728,8 +732,8 @@ namespace AutoTx
             string errMsg;
             // CurrentTransferSrc is e.g. D:\ATX\PROCESSING\2017-04-02__12-34-56\user00
             var sourceDirectory = new DirectoryInfo(_status.CurrentTransferSrc);
-            var dstPath = Path.Combine(_config.SourceDrive,
-                _config.ManagedDirectory,
+            var dstPath = Path.Combine(
+                _managedPath,
                 "DONE",
                 sourceDirectory.Name, // the username directory
                 CreateTimestamp());