In the case of an aggregate containing controlled array components,
if sliding of the indexes is involved, the components are prematurely
finalized without a corresponding initialization.

Also fix a latent bug in Exp_Aggr.Collect_Initialization_Statements
which was not always inserting Initialization_Statements properly when
the Node_After was empty (in the case of e.g. a single object
declaration).  This is needed in order to take advantage of
Initialization_Statements in Expand_N_Object_Declaration: we scan
Initialization_Statements and if a call to xxxSA is found, it means we
need to initialize the corresponding array component before it gets
prematurely adjusted.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* exp_aggr.adb (Collect_Initialization_Statements): Removed.
	(Convert_Aggr_In_Object_Decl, Expand_Array_Aggregate): Fix
	creation and insertion of Initialization_Statements.  Do not set
	Initialization_Statements when a transient scope is involved.
	Move processing of Array_Slice here.  Ensure that an object with
	an Array_Slice call gets its array component initialized.  Add
	comments.
	* exp_ch7.adb: Update comments.
	(Store_Actions_In_Scope): Deal properly with an empty list which
	might now be generated by Convert_Aggr_In_Object_Decl.
	* exp_ch3.adb: Update comments.
	(Expand_N_Object_Declaration): Remove processing of Array_Slice.