[GHC] #8818: Add withMVarMasked

[GHC]

#8818: Add withMVarMasked
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        Reporter:  hvr               |            Owner:  hvr
            Type:  feature request   |           Status:  closed
        Priority:  normal            |        Milestone:  7.8.1
       Component:  libraries/base    |          Version:
      Resolution:  fixed             |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Changes (by hvr):

 * status:  new => closed
 * resolution:   => fixed
 * milestone:  7.10.1 => 7.8.1


Comment:

 I went ahead with this (after simonmar confirmed to me on IRC this
 addition made sense).

 Also, this has been merged in the ghc-7.8 branch via [a91d68221ca30/base]

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8818#comment:2>
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