[drop dependency on MonadCatchIO-mtl
Helmut Grohne <grohne@cs.uni-bonn.de>**20150908094124
 Ignore-this: fac7d0e3c4facb314faadf88f85ca867
 
 With the fix "fix build with more recent hint or something else", we
 effectively moved from using MonadCatchIO-mtl to using exceptions, but the old
 dependency was not dropped. Drop it now.
] hunk ./igor2.cabal 27
-    MonadCatchIO-mtl >=0.2, pointless-haskell -any, exceptions
+    pointless-haskell -any, exceptions