Added "void Clear();" methods to SBDebugger, SBTarget and SBThread so they can release their shared pointers.

git-svn-id: https://llvm.org/svn/llvm-project/llvdb/trunk@109882 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/source/API/SBThread.cpp b/source/API/SBThread.cpp
index 2682705..e52496a 100644
--- a/source/API/SBThread.cpp
+++ b/source/API/SBThread.cpp
@@ -67,6 +67,13 @@
     return m_opaque_sp != NULL;
 }
 
+void
+SBThread::Clear ()
+{
+    m_opaque_sp.reset();
+}
+
+
 StopReason
 SBThread::GetStopReason()
 {