Google reported substantial performance improvement by adopting sized delete.

Tasks:

• Ensure we are building tcmalloc in a way that enables sized delete
• Ensure we are passing the c++ flags to tell the compiler to use it automatically where it can
• Make sure all of the Document/Value allocations (including RCString) can use sized delete
  • May need to make second argument to RCString::operator new() a different type (currently size_t)
• Find the best way to expose a sized free equivalent for code using malloc/relloc/free
  • Teach SharedBuffer to used sized free
  • Teach WiredTiger to use sized free for any allocations that know their own size (WT_UPDATE already identified as an important case)