Add TEXMFHOME (and friends?) to PDF.hs:showVerboseInfo.isRelevant

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While diagnosing compilation errors recently, needed to confirm pdflatex was indeed picking up my .sty files (it ended up being a latex issue, but regardless). One hypothesis I needed to discard was that pandoc had for some reason sanitized the environment -- however, the verbose output didn't give me enough information to be sure that pdflatex's kpsewhich invocations fit my expectations. (ended up using strings /proc/$PDFLATEXPID/environ with pdflatex suspended)

I specifically needed $TEXMFHOME to dispell my suspicions, but kpse* might be using several other variables -- don't know latex tooling well enough to be able to give a useful list.

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Thanks!