Fix more s3-proxy bugs (#912)
Fix more s3-proxy bugs (#912)

- Allow whatever method and headers the browser is asking for
- Modify error responses, too (the "always" keyword)
quiltdata/quilt,quiltdata/quilt-compiler,quiltdata/quilt,quiltdata/quilt,quiltdata/quilt-compiler,quiltdata/quilt-compiler,quiltdata/quilt-compiler,quiltdata/quilt,quiltdata/quilt