[GHC] #1407: Add the ability to :set -l{foo} in .ghci files

[GHC]

#1407: Add the ability to :set -l{foo} in .ghci files
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              Reporter:  guest       |            Owner:  archblob
                  Type:  feature     |           Status:  infoneeded
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:  6.6.1
             Component:  GHCi        |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by archblob):

 I have attached a fix based on HEAD.
 The fix has no test case because I'm not sure what libraries are
 guaranteed to be present on every system so that the test won't fail. If
 you can think of any, let me know and I'll add a test case or someone else
 can do it.

 I'm sorry this took a week to rebase :-P.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1407#comment:16>
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