use row_iterator for tmp rather than iterator (which was construed as std::iterator on solaris)

Author: jjallaire

inst/include/RcppParallel/RMatrix.h

@@ -41,7 +41,7 @@ class RMatrix {
          }
 
          inline row_iterator operator++(int) {
-            iterator tmp(*this); 
+            row_iterator tmp(*this); 
             operator++(); 
             return tmp;
          }