Fix buggy completion of ~/some in vi mode (#41)

This commit fixes the bug reported in:
https://github.com/att/ast/issues/682
The following sequence fails in vi mode because ksh looks in the
wrong part of the 'virtual' buffer:

$ touch ~/testfile
$ ls ~/test<tab>

The fix is to change 'virtual[i]' to 'virtual[last_virt]' in the
bugged section of code. The other changes are to make sure listing
files in a directory with something like 'ls /etc/<tab>' calls the
code for Ctrl+L to preserve 'ls /etc/' rather than try (and fail)
to complete the directory name, producing 'ls /etc\n/'. This bugfix
was backported from ksh93v- 2013-10-10-alpha.

src/cmd/ksh93/edit/vi.c
 - Backport the bugfix from ksh93v- 2013-10-10-alpha for this
   problem.

src/cmd/ksh93/tests/pty.sh
 - Add a regression test for this issue using pty, adjusted slightly
   for a fake home directory in /tmp.

src/cmd/ksh93/tests/pty.sh

@@ -453,4 +453,22 @@ w fg
 u yes-yes
 !
 
+# ======
+# err_exit #
+# Test file name completion in vi mode
+mkdir /tmp/fakehome
+tst $LINENO <<"!"
+L vi mode file name completion
+
+# Completing a file name in vi mode that contains '~' and has a
+# base name the same length as the home directory's parent directory
+# shouldn't fail.
+
+w set -o vi; HOME=/tmp/fakehome; touch ~/testfile
+w echo ~/tes\t
+u ^/tmp/fakehome/testfile\r?\n$
+!
+rm -r /tmp/fakehome
+
+# ======
 exit $((Errors<125?Errors:125))