Build with newer Boost. From Fedora.

Index: gr-blocks/lib/copy_impl.cc
--- gr-blocks/lib/copy_impl.cc.orig
+++ gr-blocks/lib/copy_impl.cc
@@ -31,6 +31,8 @@
 namespace gr {
 namespace blocks {
 
+using namespace boost::placeholders;
+
 copy::sptr copy::make(size_t itemsize)
 {
     return gnuradio::get_initial_sptr(new copy_impl(itemsize));
