Remove "using namespace std" from dwarf2reader.h. Using-directives are

forbidden by the style guide, and are bad practice in headers even under
style rules that tolerate this construct.

This fixes warnings such as:

In file included from dwarf2reader.cc:34:
dwarf2reader.h:53:17: warning: using namespace directive in global context in header [-Wheader-hygiene]
Review URL: http://breakpad.appspot.com/312002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@862 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/common/dwarf/dwarf2diehandler.cc

@@ -176,7 +176,7 @@ void DIEDispatcher::ProcessAttributeBuffer(uint64 offset,
 void DIEDispatcher::ProcessAttributeString(uint64 offset,
                                            enum DwarfAttribute attr,
                                            enum DwarfForm form,
-                                           const string& data) {
+                                           const std::string& data) {
   HandlerStack &current = die_handlers_.top();
   // This had better be an attribute of the DIE we were meant to handle.
   assert(offset == current.offset_);