_clean_input_keys() does not follow RFC2109

[eluser]BlueCamel[/eluser]
The _clean_input_keys() function in CI 1.6.2 uses the following regex to reject cookies
with "unacceptable" chars:

"/^[a-z0-9:_\/-]+$/i"

According to rfc2109 http://rfc.net/rfc2109.html the user agent may return some spacial
cookies including $Version, $Path, and $Domain. See section:

4.4 How an Origin Server Interprets the Cookie Header

In the following section 5.1 they have an example of this exchnage where the UA returns
a $Version and $Path cookie along with the cookie set by the server.

The problem here is that the regex above trips over the $ char. Can this be adjusted to
either include $ chars in the next release of CI?

This isn't a hypothetical issue as the Mathmatica web client follows the above RFC and
returns $Version ci_session $Path similar to the example in section 5.1 of the RFC.