testsuite: use binary output mode for custom curl test tools

Do not try to convert line-endings to CRLF on Windows by setting stdout
to binary mode, just like the curl tool does if --ascii is not specified.

This should prevent corrupted stdout line-ending output like CRCRLF.

In order to make the previously naive text-aware tests work with
binary mode on Windows, text-mode is disabled for them if it is not
actually part of the test case and line-endings are corrected.

tests/data/test539

@@ -8,7 +8,7 @@ FTP
 #
 # Server-side
 <reply>
-<data mode="text">
+<data>
 file contents
 </data>