bug#54614: GNU Sed 's/.../\n/' disagreement with POSIX

[Paul Eggert]

POSIX says that this shell command:

 echo 'abc' | sed 's/b/\n/g'

should output 'anc', but with GNU Sed it outputs two lines 'a' and 'c', 
even if POSIXLY_CORRECT is set.

Traditional Sed (e.g., Solaris, AIX 7) conforms to POSIX. FreeBSD Sed 
agrees with GNU Sed though, and I would guess that that GNU Sed's 
behavior is probably more expected. However, this disagreement with 
POSIX should be documented in the GNU Sed manual (and the manual should 
recommend backslash-newline over backslash-'n' for portability), and if 
POSIXLY_CORRECT is set, GNU Sed should conform to POSIX.