Build with newer Boost. From Fedora.

Index: gr-blocks/lib/mute_impl.cc
--- gr-blocks/lib/mute_impl.cc.orig
+++ gr-blocks/lib/mute_impl.cc
@@ -33,6 +33,8 @@
 namespace gr {
 namespace blocks {
 
+using namespace boost::placeholders;
+
 template <class T>
 typename mute_blk<T>::sptr mute_blk<T>::make(bool mute)
 {