[Ada] Improve error message

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on HEAD

This patch adds some more detail to messages for wrong categorization
dependencies in the most common cases. The test program

with text_io;
package wrong_cat is
  pragma pure;
end wrong_cat;

generates the messages:

wrong_cat.ads:1:06: cannot depend on "Text_IO" (wrong categorization)
wrong_cat.ads:1:06: pure unit cannot depend on non-pure unit

the second message is new

2005-09-01  Robert Dewar  <dewar@adacore.com>

	* sem_cat.adb (Check_Categorization_Dependencies): Add more detail to
	error msgs for most common cases.
	Use new errout insertion char < (conditional warning)

Attachment: difs.31
Description: Text document