PHP Fatal error: Class 'HttpRequest' not found

First, you will need to install PEAR via apt-get to get the necessary package and distribution system that both PEAR and PECL use. From a shell prompt enter: 

         sudo apt-get install php-pear        

Install the HTTP_PECL module with the following command:

sudo pecl install pecl_http

You may need to install these packages for dependencies :

apt-get install zlibc
apt-get install libcurl4-openssl-dev

Enable http.so in apache :

add "extension=http.so" to php.ini

then restart apache :

/etc/init.d/apache2 restart