Upload library, clean_file_name function: Fix xss bug.

For example: If you clear this string "%%3f3f" according to the $bad array will fail. The result will be "%3f"
Because str_replace() replaces left to right.

Signed-off-by: xeptor <servetozkan@live.com>
Remove str_replace in return
Merge pull request #2201 from xeptor/develop

Upload library, clean_file_name function: Fix xss bug.
Libraries' filenames must be named in a ucfirst-like manner
Merge branch 'develop' of github.com:EllisLab/CodeIgniter into develop
Update unit tests with the ucfirst-library-filename requirement
Fix issue #2179