Cache-Control directive case sensitivity

[mnot@…]

Currently, all of the cache-control directives (e.g., max-age) are defined as BNF strings, which means that they're case-insensitive.

However, theoretically someone could define a directive without using a string (as we do for some other constructs, e.g., the HTTP version identifier), which means that it'd be case-sensitive.

It seems that having such exceptions would be surprising, and that the most straightforward thing to do would be to define CC directive names as case-insensitive.

[mnot@…]

From [1449]:

Clarify case insensitivity of CC directives. Addresses #317.