Revert changes from GNU readline 5.0

There are two changes: one whitespace-only change in `input.c`, and
one change in `readline.c` which was (by rumor) thought to solve a
memory leak. It is, however, a no-op:

```
 #define USE_STATIC
// ...

char * readline (prompt)
const char *prompt;
{
 char *value; // was initialized with NULL before
 #ifdef USE_STATIC
  static char result[4096];
 #endif
// ...

 #ifdef USE_STATIC
  memset (result, 0, 4096);
  if (value) {
    strcpy (result, value);
    free (value);
  }
  return (strdup (result));
 #else
  return (value);
 #endif
}
```

The initialization of value with NULL GNU readline was gone, and the
code within `USE_STATIC` (and the `#define` itself) was added.

The code takes the original value that comes in `value`, copies it
into a static area `result`, and then frees the original
`value` (which assumes that `result` was allocated with `malloc`
before). The copied string is then again duplicated (which implies
creating the required size with `malloc`), and returned.

The copied string does not differ from the original one: both are
`malloc`ed and need to be `free`d by the caller.

So, this does not fix a memory leak.

Reverting this, however, makes the directory `vendor$readline/`
identical to the original GNU readline (except the `Makefile.in`
adaption, and the documentation), so that it is clean that it can be
replaced by linking to the system`'s readline.

vendor/readline/input.c

@@ -416,10 +416,10 @@ rl_read_key ()
 	  while (rl_event_hook && rl_get_char (&c) == 0)
 	    {
 	      (*rl_event_hook) ();
-	      if (rl_done) {
+	      if (rl_done)		/* XXX - experimental */
 		return ('\n');
-	      }
-	      if (rl_gather_tyi () < 0)	{
+	      if (rl_gather_tyi () < 0)	/* XXX - EIO */
+		{
 		  rl_done = 1;
 		  return ('\n');
 		}

vendor/readline/readline.c

@@ -275,17 +275,11 @@ rl_set_prompt (prompt)
 
 /* Read a line of input.  Prompt with PROMPT.  An empty PROMPT means
    none.  A return value of NULL means that EOF was encountered. */
-#define USE_STATIC
-
 char *
 readline (prompt)
-  const char *prompt;
+     const char *prompt;
 {
-  char  *value = (char *) NULL;
-#ifdef USE_STATIC
-  static char result[4096];
-#endif
-
+  char *value;
 
   /* If we are at EOF return a NULL string. */
   if (rl_pending_input == EOF)
@@ -310,17 +304,7 @@ readline (prompt)
   rl_clear_signals ();
 #endif
 
-#ifdef USE_STATIC
-  memset (result, 0, 4096);
-  if (value) {
-    strcpy (result, value);
-    free (value);
-  }
-
-  return (strdup (result));
-#else
   return (value);
-#endif
 }
 
 #if defined (READLINE_CALLBACKS)