Don't use boost::i{start,end}s_with
Don't use boost::i{start,end}s_with

Summary:
`boost::i{start,end}s_with` are locale-aware, spending unnecessary CPU time in
loading the current locale.  All this code wants to do is some case-insensitive
matching of HTTP headers, which are just ASCII.

Reviewed By: yfeldblum

Differential Revision: D4559840

fbshipit-source-id: b10c2d3ba5656bed8722d831d6ef9fd38a4d5d43

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