Use String#to_java_bytes for normal string bodies.
Lock rack integration test to rack-1.4.1.
Add rack-1.4.3 integration test.
Depend on newer version of mini_aether.
Pass through #initialze_copy, #replace to super class implementation in Environment.
Don't store fetched HTTP headers in the fronting hash because it breaks Rails' freezing the hash (this means #delete is also broken).