Purge ‘using namespace std’ from header files

std::bind and boost::lambda::bind don’t mix.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

src/crypto/crypto.h

@@ -24,7 +24,7 @@
 #include <string.h>
 #include <stdint.h>
 
-using namespace std;
+using std::string;
 
 long int myatoi( char *str );