Added schema definitions for DHCP subnet support to GASHARL

The old DHCP network object type in the gasharl schema
has been modified so that set of options can be associated
with several DHCP Subnet definitions which can be written
to dhcpd.conf in a shared network configuration.
Made dhcpEntryCustom aware of DHCP Subnet objects in gasharl schema.
Comment reformatting in ReturnVal.
Fixed unchecked operation condition in ReturnVal.

Made decodeRescanList() specify the type of the internal
vec Vector.
Reworked dhcpNetworkCustom in gasharl schema to support subnets.

The DHCP Network object type no longer requires (or permits) the network
configuration (NETWORK_NUMBER, NETWORK_MASK), to be present directly.

DHCP Network objects now contain both DHCP Option embedded objects
and DHCP Subnet embedded objects, which will contain the above
data.
Creation of the gasharl DHCP Subnet custom object class.
All non-GLOBAL DHCP Networks must have at least one subnet defined.
Reworked GASHBuilderTask to handle DHCP subnets within DCHP Network objects.
Fixed a ConcurrentModificationException in PermissionMatrixDBField.clean().
Fixed XML error reporting.
Fixed up XML error reporting a bit more.
Fixed a major regression in DBObjectTable.replaceNoSync().
Fixed subnet writing to new_dhcpd.conf in gasharl GASHBuilderTask.