patch applied (packages/mtl): restore Error constraint and fail definition if using base < 4.3

[Ross Paterson]

Fri Nov 26 08:51:12 PST 2010  Ross Paterson <ross at soi.city.ac.uk>
  * restore Error constraint and fail definition if using base < 4.3

    M ./Control/Monad/Error.hs -3 +5
    M ./mtl.cabal -1 +1

View patch online:
http://darcs.haskell.org/cgi-bin/darcsweb.cgi?r=packages/mtl;a=darcs_commitdiff;h=20101126165112-b47d3-e512933b3b7dc757c366ae534d2d65d34ad28155.gz