* einfo.ads, einfo.adb (Has_Shift_Operator): New flag.
* gnat_rm.texi: Document pragma Provide_Shift_Operators.
* interfac.ads: Minor code reorganization (add pragma
Compiler_Unit_Warning).
* par-prag.adb: Add dummy entry for Provide_Shift_Operators.
* sem_ch3.adb (Build_Derived_Numeric_Type): Copy
Has_Shift_Operator flag.
* sem_intr.adb (Check_Intrinsic_Subprogram): Make sure
Check_Shift is always called (Check_Shift): Set Has_Shift_Operator.
* sem_prag.adb: Implement pragma Provide_Shift_Operators.
* snames.ads-tmpl: Add entries for pragma Provide_Shift_Operators
Add entry for Name_Amount.
* checks.adb (Selected_Range_Checks): When checking for a null
range, make sure we use the base type, and not the subtype for
deciding a range is null.
* sem_ch5.adb (Analyze_Loop_Parameter_Specification): Check
for suspicious loop bound which is outside the range of the
loop subtype.
* gnat_ugn.texi: Add documentation section "Determining the
Chosen Elaboration Order"
* sem_ch13.adb (UC_Entry): Add field Act_Unit
(Validate_Unchecked_Conversion): Store Act_Unit
(Validate_Unchecked_Conversions): Test Warnings_Off in Act_Unit
* treepr.adb: Minor reformatting.