Because we funnel HTTP header names through the symbol table they have
to be valid VCL identifiers. It means that we can't support all valid
header names, which are tokens in the HTTP grammar. To finally close this
loophole without the help of a VMOD we allow header names to be quoted:

    req.http.regular-header
    req.http."quoted.header"

However we don't want to allow any component of a symbol to be quoted:

    req."http".we-dont-want-this

So we teach the symbol table that wildcard symbols may be quoted. There
used to be several use cases for wildcards but it is now limited to HTTP
headers.

Refs #3246
Refs #3379