move all functions in stl_utils.h into namespace butil

src/butil/stl_util.h

@@ -15,6 +15,8 @@
 
 #include "butil/logging.h"
 
+namespace butil {
+
 // Clears internal memory of an STL object.
 // STL clear()/reserve(0) does not always free internal memory allocated
 // This function uses swap/destructor to ensure the internal memory is freed.
@@ -196,8 +198,6 @@ bool ContainsKey(const Collection& collection, const Key& key) {
   return collection.find(key) != collection.end();
 }
 
-namespace butil {
-
 // Returns true if the container is sorted.
 template <typename Container>
 bool STLIsSorted(const Container& cont) {