massive updates: UTF-8 support, etc.

Sorry for the silence lately, but I've made major progress in terms of 
UTF-8 support in 1.3.5-cvs, and it's taken a while to get it to an 
easily maintainable state.  It's still not completely finished, but the 
basics (moving around, typing, deleting, backspacing, displaying the 
shortcut list at the bottom of the screen, etc.) should be working in 
the edit window and at the statusbar prompt.

As many operations as possible use multibyte strings now, so as to keep 
the most code in common between the wide and non-wide versions of nano.  
In some cases, I've used parts of David Benbennick's old UTF-8 patch, 
and in other cases I've modified parts of it or written parts of my own.  
The operations that have been converted to do this are now in their own 
source file, chars.c.  During testing, I've discovered that the non-wide 
ncurses will not display multibyte UTF-8 strings properly in UTF-8 
locales using e.g.  display_string(), and the UTF-8-enabled prereleases 
of slang 2.0 won't either under the same conditions.  In the former 
case, we can just check for and link with the wide version of ncurses, 
but I can't figure out what to do in the latter case.  (Maybe slang's 
UTF-8 support doesn't extend to its curses emulation?)

Other changes include an overhaul of the high-level statusbar input 
routines so that verbatim input works at the statusbar prompt; changes 
to verbatim input's character input mode to accept four-digit 
hexadecimal numbers instead of three-digit decimal numbers so as to 
allow input of Unicode characters; and the addition of the ability to 
cut all text from the current cursor position to the end of the file 
with one keystroke (duplicating the same functionality as in a patch for 
Pico, although I call the shortcut CutTillEnd instead of DelToEnd and 
add the alias M-T in the main list for ^X at the search prompt).