filetransfer: {up,down}load -> transfer

even the transfer function is not all that necessary since there aren't
that many users, but we'll keep it for now. we could've kept both names
but we also kind of want to use `download` for something else very soon

Change-Id: I005e403ee59de433e139e37aa2045c26a523ccbf

src/libstore/http-binary-cache-store.cc

@@ -115,7 +115,7 @@ protected:
         try {
             FileTransferRequest request(makeRequest(path));
             request.head = true;
-            getFileTransfer()->download(request);
+            getFileTransfer()->transfer(request);
             return true;
         } catch (FileTransferError & e) {
             /* S3 buckets return 403 if a file doesn't exist and the
@@ -135,7 +135,7 @@ protected:
         req.data = StreamToSourceAdapter(istream).drain();
         req.mimeType = mimeType;
         try {
-            getFileTransfer()->upload(req);
+            getFileTransfer()->transfer(req);
         } catch (FileTransferError & e) {
             throw UploadToHTTP("while uploading to HTTP binary cache at '%s': %s", cacheUri, e.msg());
         }