speed up accept header parsing a bit.

Accept header is taken from what Safari on El Capitan sends:

```ruby
require 'benchmark/ips'
require 'action_dispatch/http/mime_type'
require 'active_support/all'

accept = 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8'

Benchmark.ips do |x|
  x.report "omg" do
    Mime::Type.parse(accept)
  end
end
```

Before:

```
[aaron@TC actionpack (master)]$ be ruby ../x.rb
Calculating -------------------------------------
                 omg     3.181k i/100ms
-------------------------------------------------
                 omg     35.062k (±12.8%) i/s -    174.955k
[aaron@TC actionpack (master)]$ be ruby ../x.rb
Calculating -------------------------------------
                 omg     3.153k i/100ms
-------------------------------------------------
                 omg     33.724k (±12.4%) i/s -    167.109k
[aaron@TC actionpack (master)]$ be ruby ../x.rb
Calculating -------------------------------------
                 omg     3.575k i/100ms
-------------------------------------------------
                 omg     37.251k (±10.4%) i/s -    185.900k
```

After:

```
[aaron@TC actionpack (master)]$ be ruby ../x.rb
Calculating -------------------------------------
                 omg     3.365k i/100ms
-------------------------------------------------
                 omg     40.069k (±16.1%) i/s -    198.535k
[aaron@TC actionpack (master)]$ be ruby ../x.rb
Calculating -------------------------------------
                 omg     4.168k i/100ms
-------------------------------------------------
                 omg     47.596k (± 7.7%) i/s -    237.576k
[aaron@TC actionpack (master)]$ be ruby ../x.rb
Calculating -------------------------------------
                 omg     4.282k i/100ms
-------------------------------------------------
                 omg     43.626k (±17.7%) i/s -    209.818k
```

0 files changed, 0 insertions, 0 deletions