Implementing the notion of externally-acquirable ScriptInterpreter lock
With this notion, if parties outside the ScriptInterpreter itself need to acquire a lock on script APIs, they can do so by a pattern like this:

{
auto lock = interpeter->AcquireInterpreterLock();
// do whatever you need to do...
} // lock will automatically be released here

This might be useful for classes that use the Python convenience objects (e.g. PythonDictionary) to ensure they keep the underlying interpreter in a safe and controlled condition while they call through the C API functions
Of course, the ScriptInterpreter still manages its internal locking correctly when necessary :-)

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@178189 91177308-0d34-0410-b5e6-96231b3b80d8