fix backwards memcpy

Index: src/support/gzstream.cpp
--- src/support/gzstream.cpp.orig
+++ src/support/gzstream.cpp
@@ -32,7 +32,7 @@
 
 #include <iostream>
 #ifdef HAVE_STRING_H
-# include <string.h> // for memcpy
+# include <string.h> // for memmove
 #endif
 
 using namespace std;
@@ -92,7 +92,7 @@ int gzstreambuf::underflow() { // used for input buffe
     int n_putback = gptr() - eback();
     if ( n_putback > 4)
         n_putback = 4;
-    memcpy( buffer + (4 - n_putback), gptr() - n_putback, n_putback);
+    memmove( buffer + (4 - n_putback), gptr() - n_putback, n_putback);
 
     int num = gzread( file, buffer+4, bufferSize-4);
     if (num <= 0) // ERROR or EOF
