Add support for escaping special characters when doing filename completion.

For instance if the file name is "foo bar":
$ ls foo<TAB>
should get autocompleted to:
$ ls foo\ bar

Works for similar other characters too, which need escaping.

Also, add an accompanying test program to ensure the escaping is correct
in various scenarios (within quotes, without quotes, with other special characeters)

Thanks to Christos for reviews, help and feedback.

Start removing the WIDECHAR ifdefs; building without it has stopped working
anyway. (Ingo Schwarze)

Compile with WIDECHAR the same way the main Makefile does (Ingo Schwarze)

Userland now builds and uses terminfo instead of termcap.

OK: core@, jdc@

rename historyw -> history_w for consistency.
add wide tst code and make it the default.

Rename TEST/test.c to avoid problems when doing a cleandir on case-insensitive
file systems.
ok'ed christos.

Tokenization function enhancements:
* Make tok_init(), tok_end(), tok_reset(), tok_line() and tok_str()
publically available in <histedit.h>
* Documented the public functions in editline(3)
* Renamed tok_line() -> tok_str()
* Added new tok_line() which takes a "const LineInfo *" instead of
"const char *" (the former has "cursor" information), and optionally
return the argv index ("int *cursorc") and offset within that index
("int *cursorv"). This means that completion routines can use the
tokenization code to crack the line and easily find which word the
cursor is at. (mmm, context sensitive completion :)
* Fixed TEST/test.c when using "continuation" lines (unmatched quote
or \ at EOL), and added some more DEBUG messages including highlighting
where the cursor is (with a `_').

I got tired of typing a cc line.