QIdentityProxyModel: remove slow bounds-checking, for more performance

If we're called out of bounds, sourceModel()->index() will take care of
returning an invalid model index anyway. So calling rowCount+columnCount
every time index() is called can be avoided. These calls can be particularly
slow when sitting on top of a stack of proxymodels. And index() itself is called
very often, i.e. when a proxymodel on top of us is used by a delegate
which calls data() for many different roles.

Change-Id: I45ad6249ea6c6c719a28d25a03b6e5003f4e49ee
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
Add QMetaType::type(QByteArray) function

QMetaType::type(const char *) requires that the string argument is
0-terminated. This new overload makes it possible to query the type
of a string with an explicit length.

In particular, QByteArrays constructed by QByteArray::fromRawData(),
for example from a substring of a normalized method signature (the
"int" part of "mySlot(int"), can now be queried without making a copy
of the string.

Also, Qt5 meta-objects represent type names as QByteArray literals,
which can be fed directly to this new QMetaType::type() overload (no
need to call strlen).

Change-Id: I60d35aa6bdc0f77e0997f98b0e30e12fd3d5e100
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>