Description:
------------
For consistency with the widely known 'cd' tool and existing functionality from 
other programming languages, e.g. Perl, I believe that a call to the chdir() 
function without any parameters should be supported. In Bash and Perl, cd/chdir 
without any parameters given, changes back to the home directory of the user. As 
this is pretty convenient (because you usually start in the home directory and 
can then easier get back), I believe that such a change would also be pretty 
useful within PHP.

Test script:
---------------
# dummy script, no useful functionality
# to be executed from command line

echo "Write something:\n";
$string = trim(fgets(STDIN));
chdir('somedir');
file_put_contents('file', $string);
chdir() 
file_put_contents('file', $string);

# or just simply on the command line
php -r 'chdir();'

Expected result:
----------------
There should be no PHP warning (obviously), we should change back to the user's 
home directory and the last line

    file_put_contents('file', $string);

should then write the $string variable to /home/johndoe/file

Actual result:
--------------
$string is written to /home/johndoe/somedir/file (just as expected), however 
chdir() gives a PHP Warning:  chdir() expects exactly 1 parameter, 0 given and 
aborts the programm.