Fixed an issue where if the operating system python plug-in is changed at runtime, it wouldn't cause the process to reload the new operating system plug-in, now it does.

This is currently controlled by a setting:

(lldb) settings set target.process.python-os-plugin-path <path>

Or clearing it with:

(lldb) settings clear target.process.python-os-plugin-path 

The process will now reload the OperatingSystem plug-in.

This was implemented by:
- adding the ability to set a notify callback for when an option value is changed
- added the ability for the process plug-in to load the operating system plug-in on the fly
- fixed bugs in the Process::GetStatus() so all threads are displayed if their thread IDs are larger than 32 bits
- adding a callback in ProcessProperties to tell when the "python-os-plugin-path" is changed by the user
- fixing a crasher in ProcessMachCore that happens when updating the thread list when the OS plugin is reloaded

llvm-svn: 225831
diff --git a/lldb/source/Interpreter/OptionValueFileSpecLIst.cpp b/lldb/source/Interpreter/OptionValueFileSpecLIst.cpp
index 89d2e42..7150ad4 100644
--- a/lldb/source/Interpreter/OptionValueFileSpecLIst.cpp
+++ b/lldb/source/Interpreter/OptionValueFileSpecLIst.cpp
@@ -51,6 +51,7 @@
     {
         case eVarSetOperationClear:
             Clear ();
+            NotifyValueChanged();
             break;
             
         case eVarSetOperationReplace:
@@ -72,6 +73,7 @@
                         else
                             m_current_value.Append(file);
                     }
+                    NotifyValueChanged();
                 }
             }
             else
@@ -94,6 +96,7 @@
                     FileSpec file (args.GetArgumentAtIndex(i), false);
                     m_current_value.Append(file);
                 }
+                NotifyValueChanged();
             }
             else
             {
@@ -120,6 +123,7 @@
                         FileSpec file (args.GetArgumentAtIndex(i), false);
                         m_current_value.Insert (idx, file);
                     }
+                    NotifyValueChanged();
                 }
             }
             else
@@ -155,6 +159,7 @@
                             m_current_value.Remove (j);
                         }
                     }
+                    NotifyValueChanged();
                 }
                 else
                 {