Description:
------------
When items are removed from the realpath_cache, if the path is the same as the 
realpath, then the incorrect size is subtracted from realpath_cache_size.

This is due to the "realpath_cache_add" function. If the realpath and the path are 
the same, then an optimization occurs where bucket->realpath is assigned to the 
same location as bucket->path (so there's no copy being done). The size added to 
realpath_cache_size takes this into account, but not when removing.

This can cause the size to be incorrect and also be negative.

I've submitted a patch and some test code.

Test script:
---------------
<?php

// set the ini options to more easily reproduce
// realpath_cache_ttl = 1
// realpath_cache_siz = 16K

for($i = 0; $i < 5000; $i++) {
    file_put_contents("/tmp/foo-$i.txt", "");
    clearstatcache(true, "/tmp/foo-$i.txt");
    echo "$i - stat cache is: ".realpath_cache_size()."\n";

    if(realpath_cache_size() < 0) {
        print "Hit realpath_cache_size bug\n";
        break;
    }
}

// clean up created files
for ($x = 0; $x < $i; $x++) {
    unlink("/tmp/foo-$x.txt");
}


Expected result:
----------------
If bug is present it should output 'Hit realpath_cache_size bug'