htmlentities() should output valid ISO-8859-1 characeters to appropriate entities

Summary: Right now, when we call `htmlentities()`, we only output appropriate entities for
any ISO-8859-1 character below 0x80. Anything above, we output the empty string "".
But there is a range from 0xA0 to 0xFF that can have entities that should be output as
well.

Fixes #2186

Reviewed By: @paulbiss

Differential Revision: D1675303

Signature: t1:1675303:1415936937:4d6f5b6d74e80d7a527940b5308e4c0c9926bb24
Add missing argument to DOMXPath::{query,execute}()

Summary: These functions now take a third argument to bypass automatic context
registration. The fix is basically exactly what PHP 5 does with this argument.

Fixes #2810

Reviewed By: @JoelMarcey

Differential Revision: D1680720

Signature: t1:1680720:1415940166:d499bfa1576bfbdd54465b41f32a37fdca4e784c