"thread backtrace" should use the thread-stop-format.

<rdar://problem/28273697>

llvm-svn: 286312
diff --git a/lldb/source/Commands/CommandObjectThread.cpp b/lldb/source/Commands/CommandObjectThread.cpp
index 97f7845..e5662dd 100644
--- a/lldb/source/Commands/CommandObjectThread.cpp
+++ b/lldb/source/Commands/CommandObjectThread.cpp
@@ -277,9 +277,9 @@
 
     // Don't show source context when doing backtraces.
     const uint32_t num_frames_with_source = 0;
-
+    const bool stop_format = true;
     if (!thread->GetStatus(strm, m_options.m_start, m_options.m_count,
-                           num_frames_with_source, false)) {
+                           num_frames_with_source, stop_format)) {
       result.AppendErrorWithFormat(
           "error displaying backtrace for thread: \"0x%4.4x\"\n",
           thread->GetIndexID());