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https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man3/signal.3.html

Change more fprintf(stderr, ...); exit(...); to err[x](...). Tweak a few existing ones and fix some style.

* size_t nmemb (number of elements) first, then size_t size
* do not assume char is size 1 but use sizeof()
* allocate for char, not pointer to char (found by Michael McConville,
  fixes #261)

Closes #228.