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Works with:
- Darwin 9.8.0 (OS X 10.5.8) PPC
- Darwin 15.2.0 (OS X 10.11.2) Intel

- currently implemented for darwin and linux

err.h functions corrupts the terminal when using curses.

Closes #293.

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.