emacs: Fix digits input after completion (re: 16e4824c, e8b3274a)

Immediately after tab-completing the name of a directory, it is
not possible to type digits after the slash; ksh eats them as it
parses them as a menu selection for a nonexistent menu.

Reproducer:
$ mkdir -p emacstest/123abc
$ cd emacste[tab]123abc

Actual results:
$ cd emacstest/abc

Expected results:
$ cd emacstest/123abc

Workarounds are to press a non-numeric key followed by backspace,
or hit [tab] again to get a list of options.

Originally reported by Arnon Weinberg, 2012-12-23 07:15:19 UTC, at:
https://bugzilla.redhat.com/889745

The fix had been partially backported from ksh 93v- by AT&T
(16e4824c), which made things worse, so it was reverted (e8b3274a).
This commit backports a slightly edited version of the complete
fix. Thanks to @JohnoKing for finding the correct code. Discussion:
https://github.com/ksh93/ksh/issues/198#issuecomment-820178514

src/cmd/ksh93/edit/emacs.c: escape():
- Backport the fix for this bug that was implemented in ksh 93v-
  alpha 2013-10-10. Immediately after a slash, do not stay in "\"
  mode (file name completion) and reset the tab count.

src/cmd/ksh93/tests/pty.sh:
- Test the fix.

Resolves: https://github.com/ksh93/ksh/issues/198

src/cmd/ksh93/edit/emacs.c

@@ -1008,8 +1008,14 @@ static int escape(register Emacs_t* ep,register genchar *out,int count)
 		case '=':	/* escape = - list all matching file names */
 			ep->mark = cur;
 			if(cur<1)
+			{
 				beep();
-			else if(ed_expand(ep->ed,(char*)out,&cur,&eol,i,count) < 0)
+				return(-1);
+			}
+			ch = i;
+			if(i=='\\' && out[cur-1]=='/')
+				i = '=';
+			if(ed_expand(ep->ed,(char*)out,&cur,&eol,ch,count) < 0)
 			{
 				if(ep->ed->e_tabcount==1)
 				{
@@ -1022,7 +1028,7 @@ static int escape(register Emacs_t* ep,register genchar *out,int count)
 			else if(i=='=' || (i=='\\' && out[cur-1]=='/'))
 			{
 				draw(ep,REFRESH);
-				if(count>0)
+				if(count>0 || i=='\\')
 					ep->ed->e_tabcount=0;
 				else
 				{