* alfa.ads (Name_Of_Heap_Variable): New constant name.
* lib-xref-alfa.adb, lib-xref.adb, lib-xref.ads (Drefs): New global
table to hold dereferences.
(Add_ALFA_Xrefs): Take into account dereferences as special
reads/writes to the variable "HEAP".
(Enclosing_Subprogram_Or_Package): Move subprogram here.
(Generate_Dereference): New procedure to store a read/write dereferencew
in the table Drefs.
* put_alfa.adb (Put_ALFA): Use different default than (0,0) used for
the special "HEAP" var.
* sem_ch4.adb (Analyze_Explicit_Dereference): Store read dereference
in ALFA mode.
* sem_util.adb (Note_Possible_Modification): Store write dereference
in ALFA mode.