[patch, RFC] PR 30146, warning/errors for potentially changing values in DO loops

[Thomas Koenig]

Hello world,

the attached patch, which is not in its final stage, implements some
warnings for index variables of DO loops. For the following situations,
errors/warnings are issued when an index loop variable is
passed as an actual argument:

- If the dummy argument has INTENT(OUT). I think an error should be
   issued unconditionally.

- If the dummy argument has INTENT(INOUT). My opinion is that
   a warning should be issued unconditionally, but I am open
   to the opinions that an error would be better, or that it should
   depend on an option.

- If the dummy argument has no INTENT, or if the procedure has no
   explicit interface, I think that there should be a warning
   depending on an option (which I haven't yet implemented).

Opinions?  If there is agreement on the question of which options should
select which errors/warnings, then I will submit a final patch including
some more comments, a ChangeLog entry and a deja-gnuified test case.

	Thomas

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