Fix get_select_timezones for systems set to UTC. Solves issue #438

install/index.php::~220
```php
<div class="control-group">
	<label class="control-label"><?php echo __("Time Zone")?>:</label>
	<div class="controls">
	<?php echo get_select_timezones('TIMEZONE',cP('TIMEZONE',date_default_timezone_get()))?>
	</div>
</div>
```
The issue #438 comes from `date_default_timezone_get()`

In order of preference, the function date_default_timezone_get returns the default timezone by:

* Reading the timezone set using the date_default_timezone_set() function (if any)

* Prior to PHP 5.4.0 only: Reading the TZ environment variable (if non empty)

* Reading the value of the date.timezone ini option (if set)

* Prior to PHP 5.4.0 only: Querying the host operating system (if supported and allowed by the OS). This uses an algorithm that has to guess the timezone. This is by no means going to work correctly for every situation. A warning is shown when this stage is reached. Do not rely on it to be guessed correctly, and set date.timezone to the correct timezone instead.

If none of the above succeed, date_default_timezone_get() will return a default timezone of UTC.

This fix handle this case by forcing timezone to London City [00:00 GMT]

Hence solves issue #438