run-tests: update .t reference output after reading the test
The .t file is both test input and reference output. They should always
match. However we have different code paths to read reference output
(Test.__init__ -> Test.readrefout) and test input (TTest._run) so they might
be inconsistent if somethings change the file between those two functions.
This patch assigns "lines" read by "_run" back to "_refout" if "_refout" is
not None (with --debug, see Test.readrefout) so reference output and test
input will always match.
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