btrace, linux: fix memory leak when reading branch trace

When it takes more than one iteration to read the BTS trace, the trace from the
previous iteration is leaked.  Fix it.

2014-01-16  Markus Metzger  <markus.t.metzger@intel.com>

	* common/linux-btrace.c (linux_read_btrace): Free trace from
	previous iteration.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2014-01-16  Markus Metzger  <markus.t.metzger@intel.com>
+
+	* common/linux-btrace.c (linux_read_btrace): Free trace from
+	previous iteration.
+
 2014-01-15  Doug Evans  <dje@google.com>
 
 	* dwarf2read.c (open_and_init_dwp_file): Use pulongest to print

gdb/common/linux-btrace.c

@@ -520,6 +520,9 @@ linux_read_btrace (struct btrace_target_info *tinfo,
     {
       data_head = header->data_head;
 
+      /* Delete any leftover trace from the previous iteration.  */
+      VEC_free (btrace_block_s, btrace);
+
       /* If there's new trace, let's read it.  */
       if (data_head != tinfo->data_head)
 	{