This patch replaces exceptions of the PD session RPC interface with
result types.
The change of the quota-transfer RPC functions required the adaptation
of base/quota_transfer.h and base/child.h.
The 'alloc_signal_source' method has been renamed to 'signal_source'
to avoid an exceedingly long name of the corresponding result type.
The Pd_session::map function takes a 'Virt_range' instead of basic-type
arguments.
The 'Signal_source_capability' alias for 'Capability<Signal_source>' has
been removed.
Issue #5245
0d7d60a1f4