### Motivation:
I've now found two libraries that use Netty to be vulnerable to [CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting')](https://cwe.mitre.org/data/definitions/113.html) due to using `new DefaultHttpHeaders(false)`.
Some part of me hopes that this warning will help dissuade library authors from disabling this important security check.
### Modification:
Add documentation to `DefaultHttpHeaders(boolean)` to warn about the implications of `false`.
### Result:
This improves the documentation on `DefaultHttpHeaders`.
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