MFC r267436-267439:

• Replace malloc+memset with calloc.
• iconv_open(3): initialise ci_ilseq_invalid field of _citrus_iconv_shared struct after allocation with malloc.
• iconvlist(3): reduce a memory leak by copying strings only once.
• iconv(1):
  • Make invalids variable local to do_conv such that it prints the number of invalid characters of the current file instead of an accumulated value.
  • Make do_conv return an error when invalid characters have been found. Return EXIT_FAILURE from main if any file contained invalid characters. This matches the behaviour of GNU iconv.
  • Mark usage with __dead2 attribute.
  • Make the long_options array const.

Tested by: Pavel Timofeev <timp87@gmail.com>