Tweaked scripts.

* binutils/download.sh: Tweaked.
* cloog/download.sh: Tweaked.
* binutils/jamfile:
  * Added `srcdir-timestamp`.
  * Changed dependency on CLooG source directory to
    `binutils//srcdir-timestamp`.
* gcc/jamfile: Changed dependency on CLooG source directory, likewise as
  above.
Merge pull request #72 from Cryolite/tweakScripts

Tweaked scripts.