fixed vc7.1 iterator conversion problems

[SVN r31942]

include/boost/range/sub_range.hpp

@@ -39,21 +39,17 @@ namespace boost
     public:
         sub_range() : base() 
         { }
+
 /*		
-#if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))  
+		template< class ForwardRange2 >
-        typedef sub_range<ForwardRange> this_type;
+		sub_range( sub_range<ForwardRange2> r ) :
 
-        sub_range( this_type r ) :
+#if BOOST_WORKAROUND(BOOST_INTEL_CXX_VERSION, <= 800 )
-        : base( r )
+            base( impl::adl_begin( r ), impl::adl_end( r ) )
-        { }
+#else
+            base( r )
+#endif */
 
-        this_type& operator=( this_type r )
-        {
-            base::operator=( r );
-            return *this;
-        }
-#endif
-*/
 		template< class ForwardRange2 >
         sub_range( ForwardRange2& r ) : 
             
@@ -93,6 +89,16 @@ namespace boost
             return *this;
         }
 
+		sub_range& operator=( sub_range r )
+		{
+			//
+			// argument passed by value to avoid 
+			// const_iterator to iterator conversion
+			//
+			base::operator=( r );
+			return *this;			
+		}
+        
     public:
         
         iterator        begin()          { return base::begin(); }