Update to buildroot toolchain for nios2

Alex,

Sorry I am not good at chinese typing, and I will use english.

1. the buildroot/dl used to be created by the buildroot make.

but we will mkdir of it by hand before make.

and put all other download into it in advance.

2. the uClibc-0.9.28.tar.bz2 will be unpack to uClibc-0.9.28 without the need to specify dir name.

the busybox-snapshot.tar.bz2 will be unpack to busybox without the need to specify dir name.

you should place *bz2 in buildroot/dir, unpack , update, and repack in the dl dir.

I have just met with the people from Altera. I have asked them to setup a ftp mirror for these tools for nios2 in China, to solve the download problem. I have asked them to translate more docs into chinese, too. They have a chinse nios2 forum and chinse altera support. But I suggest them to merge, to support all native languages all over the world. If you have any suggestions, let me know, and I will forward to their high-level managements.