boost::{dynamic|static}_pointer_cast -> HPHP namespace

The primary goal here: move the custom overloads for `hphp_raw_ptr` of static/dynamic cast in `Base.h` out of the boost namespace, into HPHP namespace (which already uses normal boost versions). This means all casting, to be consistent, should happen in the HPHP namespace

Differential Revision: D959867

hphp/compiler/expression/array_element_expression.cpp

@@ -217,10 +217,10 @@ int ArrayElementExpression::getKidCount() const {
 void ArrayElementExpression::setNthKid(int n, ConstructPtr cp) {
   switch (n) {
     case 0:
-      m_variable = boost::dynamic_pointer_cast<Expression>(cp);
+      m_variable = dynamic_pointer_cast<Expression>(cp);
       break;
     case 1:
-      m_offset = boost::dynamic_pointer_cast<Expression>(cp);
+      m_offset = dynamic_pointer_cast<Expression>(cp);
       break;
     default:
       assert(false);