Add error reporting for network registration
[libqofono] Reduce the object sizes to avoid breaking ABI

Version 0.64 breaks ABI by increasing the sizes of QOfonoConnectionContext
and QOfonoMessage objects by the size of a pointer (from 12 to 16 bytes on
a 32-bit platform).
Merge pull request #55 from lpotter/errors

Add error reporting for network registration
Merge pull request #65 from monich/abi

Reduce the object sizes to avoid breaking ABI
Bump version to 0.65