Handle some different integral types is class properties.
Get signed-ness of property correct in certain situations.
Handle real value class properties.

As a side effect, this also adds support for 64bit integers.
Handle strings as class object properties.

While we are at it, fix a handling of null strings in
string expressions.
Add support for darrays as class properties.
Allow for class objects an class properties.
Merge branch 'x-mil6'