[Ada] Correct project search path when using switch -aP

[Arnaud Charlet <charlet at adacore dot com>]

gnatmake, gnatclean and the GNAT driver were incorrectly putting
directories that are specified with switches -aP<dir> after the default
project search directories in the project search path.
This patch ensures that the default project search directories are
always at the end of the project search path.

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

2013-04-24  Vincent Celier  <celier@adacore.com>

	* clean.adb (Gnatclean): Add the default project search
	directories in the project search path after scanning the
	switches on the command line.
	(Initialize): Do not put the default project search directories in the
	project search path.
	* gnatcmd.adb (GNATcmd): Add the default project search
	directories in the project search path after scanning the switches
	on the command line.
	* make.adb (Initialize): Add the default project search
	directories in the project search path after scanning the switches
	on the command line.

Attachment: difs
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