action dropdown: when label is missing, for accessibility reasons form element should at least have title

This makes sure that the animal that is specified in the URL is actually
a subdirectory inside the farm and not somewhere else in the system.
This allows that the animals are organized in different subdirectories
for more complicated farm setups.

Now the animal can be specified in the animal environment variable.

* extracted most farm code into inc/farm.php
* by default farm.php is nowhere included
* added preload.php.dist as an example farm setup
* farm.php can be included in preload.php to activate farming

same problem as in f1d7655b

string sanitization even for their own new actions

The used syntax was invalid in PHP < 3.4 and seemed to be wrong logical
as well.

Template authors now can use tpl_sidebar() to include the sidebar.
Sidebars can be defined in subnamespaces as well

\w could match multibyte chars depending on system setup

crypt seems to behave different on different systems when the salt
is empty.