Do not allocate more than necessary

Review b10cba0e0af5b1e3e8cda0201d5563f085aab2a4 and 7a16f4582da2b854a0adcba445bf6f8d750b2919:
	* lib/groupio.c (merge_group_entries): Do not allocate more than
	necessary (sizeof char* instead of char).
	Thanks for Tomáš Mráz (alioth#313962)
	* lib/groupio.c (merge_group_entries): Document that new_members
	is correctly NULL terminated. (alioth:#313940)

Align previous ChangeLog entries.
Fix translations (--home became --home-dir)

	* man/po/da.po: Fix translation (--home became --home-dir).
	* man/po/de.po: Likewise.
	* man/po/fr.po: Likewise.
	* man/po/pl.po: Likewise.
	* man/po/ru.po: Likewise.
	* man/po/sv.po: Likewise.
Fix typo in comment.
Add NEWS entries.
Fix su/1 documentation of -

	* man/su.1.xml: With getopt, '-' does not need to be the last
	option, but it is recommended for portability.
	Closes https://bugs.launchpad.net/bugs/1100775