This makes the tests easier to copy and relocate to other test numbers without having to update content. Closes #6738
... so that we can check HTTP requests for User-Agent: curl/%VERSION Update 600+ test cases accordingly. Closes #6037
which caused an error when the second header was dumped due to stdout being closed. Added test case 1066 to verify. Also fixed a potential problem where a closed file descriptor might be used for an upload when more than one URL is given.