Prevent compilation issues with boost-1.60.0.

Reported upstream at https://github.com/csound/csound/issues/570

--- Csound6.05/Opcodes/chua/ChuaOscillator.cpp	2015-04-25 14:06:22.995646234 -0500
+++ Csound6.05/Opcodes/chua/ChuaOscillator.cpp	2015-12-21 10:31:58.182362640 -0600
@@ -117,11 +117,12 @@
 //     d = sys_variables(12);
 //     gnor = a*(x.^3) + b*(x.^2) + c*x + d;
 
-#include <OpcodeBase.hpp>
 #include <boost/numeric/ublas/vector.hpp>
 using namespace boost::numeric;
 #include <cmath>
 
+#include <OpcodeBase.hpp>
+
 #undef CS_KSMPS
 #define CS_KSMPS     (opds.insdshead->ksmps)
 
uix</a></td><td class='form'><form method='get'>
<input type='hidden' name='id' value='a1537ac2bae1d7eae39188317daf1186a673e6a2'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'>