[Ada] Fix handling of symbolic links in project manager

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

Because in some places, for example in global archive dependency files,
the full resolved paths are recorded, these recorded paths may not
correspond to the original path, if ADA_PROJECT_PATH includes symbolic
links.
The test for this is to define ADA_OBJECT_PATH as a single directory with
a path that includes a symbolic link and to build, using gprmake,
a C project, giving its name on the command line relative to the directory
specified in ADA_PROJECT_PATH. Attempting to rebuild the same project
with the same command should not do anything as everything is already
up to date.

2005-11-14  Vincent Celier  <celier@adacore.com>

	* prj-ext.adb: Take into account new environment variable
	GPR_PROJECT_PATH. Warn if both GPR_PROJECT_PATH and ADA_PROJECT_PATH
	are defined.
	(Prj.Ext elaboration): For each directory in the ADA_PROJECT_PATH,
	normalize its path name, making it absolute and resolving symbolic
	links, and replace the original if resolved path is different.

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