Avoid segfault when ticky file argument is stderr
If you compiled a program with -ticky and ran it with: ./foo +RTS -rstderr -RTS the result would be a segfault. This was because the RTS interprets stderr to mean "use debugBelch to print out messages," and sets the ticky file pointer to NULL as a result, but PrintTickyInfo (the function in Ticky.c that prints out the ticky report) wasn't checking for NULL. I changed PrintTickyInfo to check whether the ticky file pointer is NULL and output to stderr if so. Also removed an unused import from CodeOutput.lhs.
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