Implement disassembler for cdb.

Filter debugging output correctly, some glitches. Extract
base class for debugging output to be able to intercept
debugging output for other purposes (such as disassembling).

src/plugins/debugger/disassemblerhandler.h

@@ -41,6 +41,8 @@ namespace Internal {
 class DisassemblerLine
 {
 public:
+    void clear();
+
     QString address;
     QString symbol;
     QString addressDisplay;