Remove generated file "src/tags" and add it to .gitignore
Fix bug which garbled the screen on multi-line scrolls.

The code to handle scroll forward and back by multiple lines
(e.g. ^U and ^D commands, or deleting a line >80 characters long)
garbled the screen. Reason: xvi used its internal lformat() routine
to put the parameters into SR and SF strings, which under terminfo
contains %p1%d instead of %d. Solution: use tgoto() to apply parameters.
Improve portability: ctags without -t and drop csh dependency