perf: always inline Program's Deref
perf: always inline Program's Deref

Shaves of a few percent on dfa heavy regexes such as `RegexSet` use.

rust-lang-nursery/regex,rust-lang/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang-nursery/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang/regex,rust-lang/regex,rust-lang-nursery/regex