fix/change DiffApplicator to allow applying several diffs

basically we need a reset-Hook before applying the next diff,
because the existing elements need to be swaped and the
position reset to start

src/lib/diff/diff-language.hpp

@@ -294,6 +294,7 @@ namespace diff{
       void
       consume (DIFF&& diff)
         {
+          target_.initDiffApplication();
           for ( ; diff; ++diff )
             diff->applyTo(target_);
         }

src/lib/diff/list-diff-application.hpp

@@ -162,10 +162,14 @@ namespace diff{
       explicit
       DiffApplicationStrategy(vector<E>& targetVector)
         : seq_(targetVector)
-        , pos_(seq_.begin())
+        { }
+      
+      void
+      initDiffApplication()
         {
-          swap (seq_, orig_);  // pos_ still refers to original input sequence, which has been moved to orig_
-          seq_.reserve (targetVector.size() * 120 / 100);    // heuristics for storage pre-allocation
+          swap (seq_, orig_);
+          seq_.reserve (orig_.size() * 120 / 100);    // heuristics for storage pre-allocation
+          pos_ = orig_.begin();
         }
     };
   

src/lib/diff/tree-diff-application.hpp

@@ -102,6 +102,9 @@ namespace diff{
           ScopeFrame(Mutator& toModify)
             : target(toModify)
             , content()
+            { }
+          
+          void init()
             {
               target.swapContent (content);
             }
@@ -298,7 +301,7 @@ namespace diff{
           
           __expect_successful_location(n);
           
-          if (srcPos()->matches(n))
+          if (not endOfData() and srcPos()->matches(n))
             ++src(); // get /after/ an explicitly given position
         }
       
@@ -328,6 +331,13 @@ namespace diff{
         {
           scopes_.emplace(mutableTargetRecord);
         }
+      
+      void
+      initDiffApplication()
+        {
+          REQUIRE (1 == scopes_.size());
+          scopes_.top().init();
+        }
     };