[cdc_rsync] Enable local syncing (#75)

Adds support for local syncs of files and folders on the same Windows
machine, e.g. cdc_rsync C:\source C:\dest. The two main changes are

- Skip the check whether the port is available remotely with PortManager.
- Do not deploy cdc_rsync_server.
- Run cdc_rsync_server directly, not through an SSH tunnel.

The current implementation is not optimal as it starts
cdc_rsync_server as a separate process and communicates to it via a
TCP port.

cdc_rsync/server_arch.h

@@ -29,10 +29,16 @@ class ServerArch {
     kWindows = 1,
   };
 
-  // Detects the architecture type based on the destination path, e.g. path
+  // Detects the arch type based on the destination path, e.g. path
   // starting with C: indicate Windows.
   static Type Detect(const std::string& destination);
 
+  // Returns the arch type that matches the current process's type.
+  static Type LocalType();
+
+  // Returns the (local!) arch specific filename of cdc_rsync[.exe].
+  static std::string CdcRsyncFilename();
+
   ServerArch(Type type);
   ~ServerArch();