[installer] apache2 fcgid.conf should place new argument inside IfModule

The installer adds MaxRequestLen 15728640 at the end of the file if it is not there (default) instead of placing it inside <IfModule mod_fcgid.c>...</IfModule>. The merge request puts it inside the IfModule block and modifies it if it exists.

configure_apache() in install/dist/lib/debian60.lib.php is not needed as install/lib/installer_base.lib.php deals with /etc/apache2/mods-available/fcgid.conf in the same way.