Import NetBSD readline.c,v 1.104: do not crash with add_history(NULL).

MFC after:	3 days
Approved by:	re (gjb)
it must be the last member, not might...

Reviewed by:	attilio
Approved by:	re (delphij, gjb)
Temporarily disable iconv for non-shared library builds.  The dynamic
loading of conversation table is not yet compatible with static builds.

Approved by:	re (gjb)
Improve bsdpatch usability:

 - Ask only once for "Apply anyway". [1]
 - Tell user what file have failed patch rather than just how
   many hunks failed.

Reported by:	jmg via pfg [1]
Tested by:	pfg [1]
Approved by:	re (gjb)
Fix bug where UART unit number was not set properly, which prevented
operation on systems with multiple serial ports. Also turn on
interrupts for the UART device, which were disabled due to a
now-fixed bug in QEMU.

Approved by:	re (gjb)