In vre2.h, include <map> and declare the map member in namespace std,

since this is no longer done via <re2/re2.h>.

src/vre2/vre2.h

@@ -32,6 +32,7 @@
 
 #ifdef __cplusplus
 
+#include <map>
 #include <re2/re2.h>
 
 using namespace re2;
@@ -39,7 +40,7 @@ using namespace re2;
 class vre2 {
 private:
 	RE2* re_;
-	map<string, int> named_group;
+	std::map<string, int> named_group;
 
 public:
 	vre2(const char *pattern, RE2::Options * const opt);