unit tests: adjust header inclusion order

Additionally, prevent multiple inclusions of curl_config.h

sources: update source headers

All C and H files now (should) feature the proper project curl source
code header, which includes basic info, a copyright statement and some
basic disc

sources: update source headers

All C and H files now (should) feature the proper project curl source
code header, which includes basic info, a copyright statement and some
basic disclaimers.

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Made unit_setup() return an error code to abort the test early

This makes it possible to skip the call to unit_stop() in such
cases. Also use Curl_safefree() in unit test 1302 so it wil

Made unit_setup() return an error code to abort the test early

This makes it possible to skip the call to unit_stop() in such
cases. Also use Curl_safefree() in unit test 1302 so it will
pass the memory torture test.

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unittest: 1303 tests Curl_timeleft

I came up with 33 different ways to call it and verify that it returns the
correct return code.