Add Q_IS_ENUM(), and provide as flag in QMetaType::typeFlags()

Add Q_IS_ENUM(), and provide as flag in QMetaType::typeFlags()

Add Q_IS_ENUM() macro to determine if a given type is an
enumeration. Use information from that in QMetaType::registerType()
to store whether custom registered metatypes are enums or not.
This information can then be accessed by calling
QMetaType::typeFlags(int type). This is used by the declarative
code to determine whether a custom type in a variant can be safely
cast to an integer, which is required to allow passing non-local
enums as signal/slot params.

Change-Id: I9733837f56af201fa3017b4a22b761437a3c0de4
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>