Loading package gnuidn-0.2.1 ... 

GHCi runtime linker: fatal error: I found a duplicate definition for symbol
   c_isascii
whilst processing object file
   /usr/local/lib/libidn.a
This could be caused by:
   * Loading two different object files which export the same symbol
   * Specifying the same object file twice on the GHCi command line
   * An incorrect `package.conf' entry, causing some object to be
     loaded twice.
GHCi cannot safely continue in this situation.  Exiting now.  Sorry.

Failed to install git-annex-5.20150113
cabal: user error (Error: some packages failed to install:
git-annex-5.20150113 failed during the building phase. The exception was:
ExitFailure 1