[GHC] #9230: Make -fwarn-tabs the default

[GHC]

#9230: Make -fwarn-tabs the default
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        Reporter:  dfeuer            |                   Owner:  mlen
            Type:  feature request   |                  Status:  closed
        Priority:  normal            |               Milestone:  7.10.1
       Component:  Compiler          |                 Version:  7.8.2
      Resolution:  fixed             |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D255,
                                     |  Phab:D399
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Comment (by yokto):

 This default is clearly in favour of people using spaces. A more neutral
 option would be to just warn when character counts and tabs are being
 mixed.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9230#comment:35>
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