Fixes for Konsole

• Increase the limit of the disk-backed "unlimited" scrollback option via use of 64bit ints and file offset. This remedies the problem where the recent history was not stored once the file reached 2GB, which manifested as a blank window when scrolling up.
• correct width of blinking cursor for wide characters (KDE bug #318453)

Reviewed by: tcberner
Approved by: swills (mentor)
Obtained from: KDE (cursor fix)
Differential Revision: https://reviews.freebsd.org/D9758