simplify port-actual allocation, separate allocation from initialization
on ICE, print file-line number in decimal, please
replaced per-intsance calls to unroll_ports with copy-from-template idiom
code state is still messy with #if conditional, so clean it up next
partial clean-up, introducing typedef for target_context (footprint&)
intended for port unrolling
another round of cleanup, using adaptor function as_target_context()
Merge branch 'port-allocation-rewrite'
perm'd CACHE_SUBSTRUCTURES_IN_FOOTPRINT:1
perm'd BOOL_CONNECTIVITY_CHECKING:1
perm'd PROCESS_CONNECTIVITY_CHECKING:1
perm'd FOOTPRINT_OWNS_CONTEXT_CACHE:1
perm'd AGGREGATE_PARENT_REFS:1
perm'd IMPLICIT_SUPPLY_PORTS:1
perm'd PRS_SUPPLY_OVERRIDES:1
perm'd PRS_SUBSTRATE_OVERRIDES:1
perm'd INSTANCE_SUPPLY_OVERRIDES:1
perm'd BOOL_PRS_CONNECTIVITY_CHECKING:1