fixing malformed Accept-Encoding header in r.http
Merge branch 'next' into sam_datum_minarchy
Implemented datum_array_builder_t::insert and splice (copy/pasting from datum_t).
Added erase_range and erase to datum_array_builder_t.
Moved datum_array_builder_t methods to cc files.
Removed use of datum_ptr_t in arr.cc functions.
Removed the unused type datum_ptr_t.