Call to undefined function curl_init appears when you dont have installed php5-curl or its not enabled.
How to enable php5-curl
Navigate to /etc/php5/conf.d and open curl.ini and then remove the comment from the extension directive. It should look like something this.
; configuration for php CURL module
extension=curl.so
Save the file. Restart apache
#service apache2 restart
How to Install php5-curl
#apt-get install php5-curl
Restart Apache
linux apache mysql php 
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