Make all tests pass, couple of changes

I had a little issue with pathologic and wanted to create tests for this case. But even before starting to work on this I started the "Pathologic path filtering" test case to see the result. It showed 5 fails, 4 with 'Path with just slash' and one with '"Also considered local" paths'.

The modification to make the "path with just slash" was pretty simple:

if ($parts['trimmed_path'] === '') {
# become
if ($parts['trimmed_path'] === '' || $parts['trimmed_path'] === '/') {

The '"Also considered local" paths' was much harder to get pass.

# there was a typo in the test:
'local_paths' => "http://example.com/qux\nexample.org\/bananas",
#become
'local_paths' => "http://example.com/qux\nexample.org\n/bananas",

# i also added a clean_url reset before making the last tests
variable_set('clean_url', TRUE);

In the _pathologic_filter function the $parts needed to be rebuild if the expolded path was just a domain. This was especially done for the example.org path in the '"Also considered local" paths' test.

In _pathologic_replace the local_path is kept in a variable. This was needed to clean the url in cases where the local path point to a subdirectory (http://example.com/qux).