I also needed the line:
apt-get install php5-json
in order to get past the blank screen while installing Moodle locally on one Ubuntu 13.10 desktop.
I have added this line to the documentation page at http://docs.moodle.org/26/en/Installation_on_Ubuntu_using_Git
After adding this module and restarting apache my Moodle 2.6.1 installation went past the blank screen and worked nicely.