remove unneeded try/catch blocks

they were just catching and rethrowing
use DOKU_LF

PHP_EOL is platform dependent, so you get in trouble while migrating
between platforms.
better filename parsing

The filename found in the URL will be used for old plugins missing a
base entry in their plugin.info.txt and lacking a subdirectory inside
the archive as well. This patch makes sure possible query strings aren't
included in the filename.

Note: io_download() will also try to get a filename from any
content-disposition header.

If no filename can be found we simply use an md5 sum of the URL and hope
the plugin will contain it's own hint for naming.
added missing localization