[Issue 18528] New: dmd should deduplicate identical errors

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18528

          Issue ID: 18528
           Summary: dmd should deduplicate identical errors
           Product: D
           Version: D2
          Hardware: x86
                OS: Mac OS X
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: timothee.cour2 at gmail.com

eg:
/Users/timothee/git_clone/D/ggplotd/source/ggplotd/geom.d(117,24): Deprecation:
module `ggplotd.aes` member hasAesField is not visible from module geom
/Users/timothee/git_clone/D/ggplotd/source/ggplotd/geom.d(117,24): Deprecation:
module `ggplotd.aes` member hasAesField is not visible from module geom

dmd should deduplicate error messages and print:

/Users/timothee/git_clone/D/ggplotd/source/ggplotd/geom.d(117,24): Deprecation:
module `ggplotd.aes` member hasAesField is not visible from module geom

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