Fix some compilation warnings

src/boost-workaround/boost/graph/graphml.hpp

@@ -162,7 +162,7 @@ public:
                  (name, m_dp, graph_property_tag(), value, value_type,
                   type_found));
         }
-        catch (bad_lexical_cast)
+        catch (bad_lexical_cast&)
         {
             throw parse_error("invalid value \"" + value + "\" for key \"" +
                               name + "\" of type \"" + value_type + "\"");
@@ -188,7 +188,7 @@ public:
                  (name, m_dp, any_cast<vertex_descriptor>(vertex),
                   value, value_type, type_found));
         }
-        catch (bad_lexical_cast)
+        catch (bad_lexical_cast&)
         {
             throw parse_error("invalid value \"" + value + "\" for key " +
                               name + " of type " + value_type);
@@ -214,7 +214,7 @@ public:
                  (name, m_dp, any_cast<edge_descriptor>(edge),
                   value, value_type, type_found));
         }
-        catch (bad_lexical_cast)
+        catch (bad_lexical_cast&)
         {
             throw parse_error("invalid value \"" + value + "\" for key " +
                               name + " of type " + value_type);

src/graph/gml.hh

@@ -163,7 +163,7 @@ public:
             {
                 id = boost::get<double>(_stack.back().second["id"]);
             }
-            catch (bad_get)
+            catch (bad_get&)
             {
                 throw gml_parse_error("invalid node id");
             }
@@ -195,7 +195,7 @@ public:
                 source = boost::get<double>(_stack.back().second["source"]);
                 target = boost::get<double>(_stack.back().second["target"]);
             }
-            catch (bad_get)
+            catch (bad_get&)
             {
                 throw gml_parse_error("invalid source and target ids");
             }

src/graph/graphml.cpp

@@ -293,7 +293,7 @@ private:
             {
                 id = lexical_cast<size_t>(std::string(v,1));
             }
-            catch (bad_lexical_cast)
+            catch (bad_lexical_cast&)
             {
                 std::stringstream s;
                 s << "on line " << XML_GetCurrentLineNumber(m_parser)