Sync with FPS head, including the following patches:

Sync with FPS head, including the following patches:

    Thu May 18 15:45:46 EST 2006  sjanssen@cse.unl.edu
      * Export unsafeTake and unsafeDrop

    Fri May 19 11:53:08 EST 2006  Don Stewart <dons@cse.unsw.edu.au>
      * Add foldl1'

    Fri May 19 13:41:24 EST 2006  Don Stewart <dons@cse.unsw.edu.au>
      * Add fuseable scanl, scanl1 + properties

    Fri May 19 18:20:40 EST 2006  Don Stewart <dons@cse.unsw.edu.au>
      * Spotted another chance to use unsafeTake,Drop (in groupBy)

    Thu May 18 09:24:25 EST 2006  Duncan Coutts <duncan.coutts@worc.ox.ac.uk>
      * More effecient findIndexOrEnd based on the impl of findIndex

    Thu May 18 09:22:49 EST 2006  Duncan Coutts <duncan.coutts@worc.ox.ac.uk>
      * Eliminate special case in findIndex since it's handled anyway.

    Thu May 18 09:19:08 EST 2006  Duncan Coutts <duncan.coutts@worc.ox.ac.uk>
      * Add unsafeTake and unsafeDrop
      These versions assume the n is in the bounds of the bytestring, saving
      two comparison tests. Then use them in varous places where we think this
      holds. These cases need double checking (and there are a few remaining
      internal uses of take / drop that might be possible to convert).
      Not exported for the moment.

    Tue May 16 23:15:11 EST 2006  Don Stewart <dons@cse.unsw.edu.au>
      * Handle n < 0 in drop and splitAt. Spotted by QC.

    Tue May 16 22:46:22 EST 2006  Don Stewart <dons@cse.unsw.edu.au>
      * Handle n <= 0 cases for unfoldr and replicate. Spotted by QC

    Tue May 16 21:34:11 EST 2006  Don Stewart <dons@cse.unsw.edu.au>
      * mapF -> map', filterF -> filter'