This patch improves the handling of array aggregates with static components.
It allows constant folding of aggregates with a single association given by
an expanded name, and it allows in-place assignments for aggregates when the
array type has an index type that has a non-standard representation.

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

2010-10-21  Ed Schonberg  <schonberg@adacore.com>

	* exp_aggr.adb (Flatten): An association for a subtype may be an
	expanded name.
	(Safe_Left_Hand_Side): An unchecked conversion is part of a safe
	left-hand side if the expression is.
	(Is_Safe_Index): new predicate
	Minor clean up in identier names (Indices -> Indexes).
	* exp_ch3.adb (Expand_Freeze_Enumeration_Type): Indicate that the
	generated Rep_To_Pos function is a Pure_Function.