screen: Introduce Xx string escape showing the executed command of a window

either only the executed command ('X') or the whole command line ('x') of
each window is shown.

Signed-off-by: Thomas Renninger <address@hidden>

--- ./doc/screen.1.orig	2013-09-13 13:26:28.055279274 +0000
+++ ./doc/screen.1	2013-09-13 13:26:41.385279250 +0000
@@ -3747,6 +3747,10 @@ window; with '+' qualifier: starting wit
 one.
 .IP W
 all window numbers and names except the current one
+.IP x
+the executed command including arguments running in this windows
+.IP X
+the executed command without arguments running in this windows
 .IP y
 last two digits of the year number
 .IP Y
--- ./screen.c.orig	2013-09-13 13:26:28.057279274 +0000
+++ ./screen.c	2013-09-13 13:34:30.151278421 +0000
@@ -2693,6 +2693,20 @@ int rec;
 	    }
 	  p += strlen(p) - 1;
 	  break;
+	case 'X': case 'x':
+	  *p = 0;
+	  for (i = 0; win && win->w_cmdargs[i]; i++)
+	    {
+	      if (l < strlen(win->w_cmdargs[i]) + 1)
+		break;
+	      sprintf(p, i ? "%s" : " %s", win->w_cmdargs[i]);
+	      l -= strlen(p);
+	      p += strlen(p);
+	      if (i == 0 && *s == 'X')
+		break;
+	    }
+	  p--;
+	  break;
 	case 'l':
 #ifdef LOADAV
 	  *p = 0;