Make all foreign key constraints deferrable

This will be required later, when the load routine will temporarily delete
referenced rows to insert new versions of them.

constraints.sql

@@ -33,13 +33,13 @@ alter table change_parents add constraint source_file_id_valid
 
 -- checking all change number references are valid
 alter table rev add constraint rev_change_valid
-      foreign key (change) references change;
+      foreign key (change) references change deferrable;
 
 alter table revcx add constraint revcx_change_valid
-      foreign key (change) references change;
+      foreign key (change) references change deferrable;
 
 alter table change_branches add constraint change_branches_change_valid
-      foreign key (change) references change;
+      foreign key (change) references change deferrable;
 
 -- p4users primary key
 alter table p4user
@@ -54,27 +54,27 @@ select * from change_desc where not exists
 
 -- checking all depotpaths + revnums are valid
 alter table revcx add constraint revcx_depot_rev_valid
-      foreign key (depotpath, revision) references rev;
+      foreign key (depotpath, revision) references rev deferrable;
 alter table rev_marks add constraint rev_marks_depot_rev_valid
-      foreign key (depotpath,revision) references rev;
+      foreign key (depotpath,revision) references rev deferrable;
 
 -- set up safety constraints for later additions
 alter table change_marks add constraint change_marks_branch_valid
-      foreign key (branchpath,change) references change_branches;
+      foreign key (branchpath,change) references change_branches deferrable;
 
 create unique index change_parents_unique on change_parents
 	(branchpath,change,parent_branchpath,parent_change,ref);
 alter table change_parents add constraint change_branchpath_valid
       foreign key (branchpath,change)
-      references change_branches;
+      references change_branches deferrable;
 alter table change_parents add constraint change_parents_valid
       foreign key (parent_branchpath, parent_change)
-      references change_branches(branchpath, change);
+      references change_branches(branchpath, change) deferrable;
 create unique index change_parents_sanity
        on change_parents(change, branchpath, parent_branchpath,
        parent_change, manual);
 
--- create indexes
+-- create indexes:
 create index integed_change_idx on integed (change);
 create index integed_subject_idx on integed (subject, subject_maxrev);
 create index integed_object_idx on integed (object, object_maxrev);
@@ -99,7 +99,7 @@ group by
 
 -- checking all change number references are valid
 alter table change add constraint change_who_user_valid
-      foreign key (who_user) references p4user;
+      foreign key (who_user) references p4user deferrable;
 
 -- the 'integed' table is denormalised, with rows normally appearing
 -- in pairs.  However, these rows were missing their partners: