Eliminated "handled" field in Parser::Action

This field was used during development to measure the
coverage of the ANSI terminal parser against typical
terminal input sequences.

The "handled" field has not been read by any code since
commit 1ee54cd7 (February 2011). Eliminating the field
by popular request (closes #723).

src/terminal/parseraction.h

@@ -46,7 +46,6 @@ namespace Parser {
   public:
     wchar_t ch;
     bool char_present;
-    mutable bool handled;
 
     std::string str( void );
 
@@ -56,7 +55,7 @@ namespace Parser {
 
     virtual bool ignore() const { return false; }
 
-    Action() : ch( -1 ), char_present( false ), handled( false ) {};
+    Action() : ch( -1 ), char_present( false ) {};
     virtual ~Action() {};
 
     virtual bool operator==( const Action &other ) const;