[Ada] -aP switch for gnatmake

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

A new switch -aP<dir> is added for gnatmake and gprmake to add
directories in the project search path. The test for this is to have a
project A importing a project B just with its file name, where project
file B is neither in the same directory as project file A nor in one
of the directory specified in GPR/ADA_PROJECT_PATH, and to use the new
switch -aP with the project directory of B.

This patch also allows the project path logical names on VMS to support
the use of VMS specific file name conventions and the use of multiple
equivalences.

2007-06-06  Vincent Celier  <celier@adacore.com>

	* prj.adb (Project_Empty): Gives default value for new component
	Libgnarl_Needed

	* prj-attr.ads: Minor reformatting

	* prj-env.ads, prj-env.adb (For_All_Object_Dirs): Register object
	directory using the untouched casing.
	(For_All_Source_Dirs): Idem.

	* prj-ext.ads, prj-ext.adb (Search_Directories): New table to record
	directories specified with switches -aP.
	(Add_Search_Project_Directory): New procedure
	(Initialize_Project_Path): Put the directories in table
	Search_Directories in the project search path.
	(Initialize_Project_Path): For VMS, transform into canonical form the
	project path.

Attachment: difs
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