Simplify saved_command_line handling

There doesn't seem to be much point in trying to reuse this buffer.
Prefer simplicity instead.

(In case you're wondering whether this fixes an off-by-one: linelength
is misnamed; it's really a size including terminating null char.)

gdb/ChangeLog:
2016-03-09  Pedro Alves  <palves@redhat.com>

	* event-top.c (command_line_handler): Use xfree + xstrdup instead
	of xrealloc + strcpy.
	* main.c (captured_main): Use xstrdup instead of xmalloc plus
	manual clear.
	* top.c (saved_command_line): Rewrite comment.
	(saved_command_line_size): Delete.
	(command_line_input): Use xfree + xstrdup instead of xrealloc +
	strcpy.
	* top.h (saved_command_line_size): Delete declaration.

gdb/ChangeLog

@@ -1,3 +1,15 @@
+2016-03-09  Pedro Alves  <palves@redhat.com>
+
+	* event-top.c (command_line_handler): Use xfree + xstrdup instead
+	of xrealloc + strcpy.
+	* main.c (captured_main): Use xstrdup instead of xmalloc plus
+	manual clear.
+	* top.c (saved_command_line): Rewrite comment.
+	(saved_command_line_size): Delete.
+	(command_line_input): Use xfree + xstrdup instead of xrealloc +
+	strcpy.
+	* top.h (saved_command_line_size): Delete declaration.
+
 2016-03-09  Pedro Alves  <palves@redhat.com>
 
 	* event-top.c: Include buffer.h.

gdb/event-top.c

@@ -650,13 +650,8 @@ command_line_handler (char *rl)
   /* Save into global buffer if appropriate.  */
   if (repeat)
     {
-      if (linelength > saved_command_line_size)
-	{
-	  saved_command_line
-	    = (char *) xrealloc (saved_command_line, linelength);
-	  saved_command_line_size = linelength;
-	}
-      strcpy (saved_command_line, linebuffer);
+      xfree (saved_command_line);
+      saved_command_line = xstrdup (linebuffer);
       if (!more_to_come)
 	{
 	  command_handler (saved_command_line);

gdb/main.c

@@ -506,8 +506,7 @@ captured_main (void *data)
   ndir = 0;
 
   clear_quit_flag ();
-  saved_command_line = (char *) xmalloc (saved_command_line_size);
-  saved_command_line[0] = '\0';
+  saved_command_line = (char *) xstrdup ("");
   instream = stdin;
 
 #ifdef __MINGW32__

gdb/top.c

@@ -125,11 +125,9 @@ char *current_directory;
 /* The directory name is actually stored here (usually).  */
 char gdb_dirbuf[1024];
 
-/* Buffer used for reading command lines, and the size
-   allocated for it so far.  */
-
+/* The last command line executed on the console.  Used for command
+   repetitions.  */
 char *saved_command_line;
-int saved_command_line_size = 100;
 
 /* Nonzero if the current command is modified by "server ".  This
    affects things like recording into the command history, commands
@@ -1222,13 +1220,8 @@ command_line_input (const char *prompt_arg, int repeat, char *annotation_suffix)
   /* Save into global buffer if appropriate.  */
   if (repeat)
     {
-      if (linelength > saved_command_line_size)
-	{
-	  saved_command_line
-	    = (char *) xrealloc (saved_command_line, linelength);
-	  saved_command_line_size = linelength;
-	}
-      strcpy (saved_command_line, linebuffer);
+      xfree (saved_command_line);
+      saved_command_line = xstrdup (linebuffer);
       return saved_command_line;
     }
 

gdb/top.h

@@ -22,7 +22,6 @@
 
 /* From top.c.  */
 extern char *saved_command_line;
-extern int saved_command_line_size;
 extern FILE *instream;
 extern int in_user_command;
 extern int confirm;