Disabling PHP Deprecation Warnings and Notices
Solution 1:
First of all I want to thank binfalse for answering this question, however my problem was not solved with his suggestion and notices continued to show.
This is because PHP has several places where configuration can be set. While I had an idea of the precedence of those settings, I decided to test them experimentally to be sure of what I am going to say in this answer.
So here is a list of those places, from the more global to the more specific. Each setting lower in the list can override a setting that come before.
The php.ini configuration file. In case of Ubuntu there are two of them, /etc/php5/apache2/php.ini is the one used for php apache module. It will have a global effect on all virtual hosts.
The conf.d directory. Actually not all installations will have this modularized configuration, but in case of Ubuntu is located in /etc/php5/apache2/conf.d for the apache module. Any file added in this directory is going to be added to main php.ini configuration with higher precedence than php.ini. In other words any setting here will override settings in php.ini - I tested adding an error.ini. It will have a global effect on all vitual hosts.
Apache virtual host configuration. Generally set in /etc/apache2/sites-available, every virtual host can have different settings. Inside the VirtualHost tag it's possible to include "php_value error_reporting ", where value is the numeric result of the boolean operations on the constants. In this configuration, in fact is not allowed to use the mnemonic constants but only a numeric value. It will affect only a single virtual host. It will override above settings.
.htaccess. It's also possible to set configuration values and in particular the error_reporting setting also in .htaccess, with the same syntax described in 3. It will affect only the directory in which .htaccess is located and all subdirectories. It will override above settings, in this case is not necessary to restart apache.
Source code. The last place where this setting can be altered is directly in the executed PHP source. If used, will override all previous settings, and that's exactly what I was facing. It can be set calling the function "error_reporting()" or with "ini_set("error_reporting", )". Compile errors could still show, because the script won't be executed in that case.
Solution 2:
Set the variable in /etc/php5/apache2/php.ini
to
error_reporting = E_COMPILE_ERROR|E_RECOVERABLE_ERROR|E_ERROR|E_CORE_ERROR
this will only show errors.