The special expansion done in GNATprove mode should be adapted to slices
where the prefix has access type, like indexed expressions.

There is no impact on compilation.

2019-08-20  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* exp_spark.adb (Expand_SPARK_N_Slice_Or_Indexed_Component):
	Renaming of function to apply to slices as well.
	(Expand_SPARK): Expand prefix of slices of access type.

From-SVN: r274740