DOC: documentation on http header capture is wrong

DOC: documentation on http header capture is wrong

Since commit it is said that only the first value of the first occurrence
of a header is captured. This is wrong. Since the introduction of header
captures in version 1.1 in 2005 (commit e983144d), the WHOLE line of the
LAST occurrence has been captured and the behaviour has never changed.

At this time the doc was correct. The error was introduced in the new doc
in 1.3.14 in 2007 (commit 0ba27505).

So this fix should be backported to 1.4 and 1.3.