Clarify point about always NUL-terminating.

errors specified by the library routine malloc(3)).

- s/MESSAGES/DIAGNOSTICS/, and put message descriptions in a nice list.
- Talk more about how using malloc() in signal handlers is bad.

Markus Friedl.

commit, as we want our documentation to be as consistently formatted as
possible (it's getting there :-)).

least, this is the impression I get from looking at a lot of Perl docs.

calloc(), and realloc().  Idea from NetBSD.

(K&R-style type promotions are evil),

their own malloc() implementation.

didn't do so for us.  By default, malloc() zeros out the space it
allocates but the programmer cannot rely on this as it is implementation-
specific (and configurable via /etc/malloc.conf)

- avoid .Xref to one's own manpage

from conversations between various people