Update for zlib and bzip2 installation instructions

[gerard@…]

From Zack Winkles:

10. Build proper bzip2 libraries. We build the correct libbz2.so, as the Makefile adds -fPIC by itself, but then we simply run make, which adds all this PIC code into a static libbz2.a, which is completely unnecessary and unoptimal. In doing this, we slow down anything that uses libbz2.a by 20%. The ONLY thing needed to build a proper libbz2.a and libbz2.so is to make clean right after make -f Makefile-libbz2_so. The make clean leaves bzip2-shared and libbz2.so* intact, so there is no harm, only gain.

11. Build proper zlib libraries. The reasoning behind this is the exact same as that of libbz2, but the procedure is a bit more involved. The following commands do what we need:

CFLAGS="$CFLAGS -fPIC" ./configure --prefix=/usr --shared make make install make clean ./configure --prefix=/usr make make install