Don't use QFile's Qt3support member, use fileName() instead.

Reviewed-by: Trust me

The QFileNetworkReply is a wrapper around QFile that
has therefore similar performance. This avoids
the usage of the unperformant QNetworkAccessFileBackend.

The benchmark qfile_vs_qnetworkaccessmanager shows
that the QFileNetworkReply's performance is better
than 0.9x of QFile compared to QNetworkAccessFileBackend
which had about 0.5x of QFile.

Reviewed-by: Peter Hartmann

The QDateTimeParser forces at least two QString allocations
to convert the Month string into a integer. This makes parsing
the date string the most expesnsive operation from within
replyHeaderChanged.

Use sscanf to parse the RFC1123 header to get a significant
speedup. Use a switch case statement to convert the month
name to a integer.

Reviewed-By: Markus Goetz

toLower will force a memory allocation, and memory allocations
are certainly adding a delay. Use qstricmp were this is easily
possible. This change makes headerValues et all drop out of
the profile.

QChar::toLower will now be called more often, specially for
loops that do linear searching. In the profile with real web
content this is faster than using QByteArry::toLower in the
inner loop and the forced memory allocations.

Reviewed-By: Markus Goetz

Using qstricmp is faster on the desktop than the alloc of
QByteArray::toLower and the QByteArray::operator==.

QChar::toLower will now be called for the input key from
within the loop. In the measurements done this is still
a performance improvement over the allocation done by
QByteArray::toLower. For more header values this might
not be the case anymore.

RESULT : tst_Loading::byteArrayTestLower():
     0.00076 msec per iteration (total: 25, iterations: 32768)
RESULT : tst_Loading::byteArrayTestCompare():
     0.00028 msec per iteration (total: 37, iterations: 131072)

Reviewed-By: Markus Goetz

HTTP header names are case insensitive, but stick to what all browsers
etc. use to work around buggy servers.

Reviewed-by: TrustMe

HTTP header names are case insensitive, but stick to what all browsers
etc. use to work around buggy servers.

Task-number: QTBUG-5618
Reviewed-by: Peter Hartmann