Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

A set of MFCs allowing stable/9 to be built again on head after r250881:

r250227:
Improve compatibility with recent flex from flex.sourceforge.net.

r250914:
Improve compatibility with old flex and fix build with GCC.

r250926 (partial):
Work around build breakages with GCC 4.2.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Fix some more warnings found by clang.

- Fix signal handling in bc/dc. Now Ctrl-C terminates the execution.

Requested by: gk (via private mail)
Approved by: delphij (mentor)

Fix a bug in previous revision.

The bc(1) program may need to deal with files when it's being run in
interactive mode, so we can not blindly use interactive mode (in turn
use libedit) but need to check if the input source is really the standard
input.

This commit should fix a regression where 'bc -l' would not parse the
mathlib.

Reported by: trasz

Use libedit when interacting with tty, which provided history
functionality, etc. as did by GNU bc.

This also fixes an issue where BSDL bc can not handle very long
line.

Reported by: imp
Reviewed by: imp

- style(9)

Approved by: delphij (mentor)

Replace GNU bc/dc with BSDL versions ported from OpenBSD. They have a good
compatibility level with the GNU counterparts and have shown to be mature
enough. For now, the GNU versions aren't removed from the tree, just detached
from the build.

Sponsored by: Google Summer of Code 2008
Portbuild run by: erwin
Approved by: delphij