printf() is a horrible interface as it does no type checking.
Let's at least use the compiler to check format strings and
arguments. This obviously doesn't work for translated strings
and using report_error on translated strings is dubious. But OK.
Had to convert a number of report_error() calls to supress
warnings.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
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