patch applied (ghc): make exit() overridable, for use in DLLs

[Simon Marlow]

Wed Aug  9 02:24:39 PDT 2006  Simon Marlow <simonmar at microsoft.com>
  * make exit() overridable, for use in DLLs
  See #753

    M ./includes/RtsAPI.h +2
    M ./rts/RtsStartup.c +4
    M ./rts/Storage.c -1 +1