MEDIUM: checks: Support matching on headers for http-check expect rules

MEDIUM: checks: Support matching on headers for http-check expect rules

It is now possible to add http-check expect rules matching HTTP header names and
values. Here is the format of these rules:

  http-check expect header name [ -m <meth> ] <name> [log-format] \
                           [ value [ -m <meth> ] <value> [log-format] [full] ]

the name pattern (name ...) is mandatory but the value pattern (value ...) is
optionnal. If not specified, only the header presence is verified. <meth> is the
matching method, applied on the header name or the header value. Supported
matching methods are:

  * "str" (exact match)
  * "beg" (prefix match)
  * "end" (suffix match)
  * "sub" (substring match)
  * "reg" (regex match)

If not specified, exact matching method is used. If the "log-format" option is
used, the pattern (<name> or <value>) is evaluated as a log-format string. This
option cannot be used with the regex matching method. Finally, by default, the
header value is considered as comma-separated list. Each part may be tested. The
"full" option may be used to test the full header line. Note that matchings are
case insensitive on the header names.