Ttrick makepkg not do re-download already existing packages (AUR)

When building from AUR, makepkg may re-download already existing files. To prevent this, in PKGBUILD point source array to existing filename. ie:

from:

source=('http://dlc.sun.com.edgesuite.net/netbeans/7.3.1/final/zip/netbeans-7.3.1-201306052037-php.zip'
        'netbeans.desktop')

to:

source=('netbeans-7.3.1-201306052037-php.zip'
        'netbeans.desktop')