DOC: add some information on capture.(req|res).hdr

Clarify the beginning of the index.
MINOR: http: capture.req.method and capture.req.uri

Add 2 sample fetchs allowing to extract the method and the uri of an
HTTP request.

FIXME: the sample fetches parser can't add the LW_REQ requirement, at
the moment this flag is used automatically when you use sample fetches.

Note: also fixed the alphabetical order of other capture.req.* keywords
in the doc.
BUG/MINOR: tcpcheck connect wrong behavior

A typo made first step of a tcpcheck to be a connect step. This patch
prevents this behavior. The bug was introduced in 1.5-dev22 with
"tcp-check connect" and only affects these directives. No backport is
needed.