enable gd support in php

For the new user, it's very common that will have problem to enable gd support in php, after fail and retry for hours, I figured out to use the steps below to get it work:
1. download/compile/install libpng
2. checkout the libjpeg if you can't get access to their website:
cvs -z3 -d:pserver:anonymous@libjpeg.cvs.sourceforge.net:/cvsroot/libjpeg co -P modulename
3. compile/install libjpeg
4. run "make clean" at the source directory of php (important, otherwise you will run into some weired error)
5. the configure for php should be like this:(use the exact directory suits your environment)
./configure --with-mysql --with-gd --with-apxs=/usr/local/apache/bin/apxs --with-jpeg-dir=/usr/local/lib

