list all missing extensions

Previously, when more than one extensions are missing, it asked you to install the first missing extension, and said nothing about the other missing extensions. this behavior can be misleading.
handling of query string in manifest media URLs

Media URLs in the manifest can contain query string (called "auth" here), e.g. <media url="some?name=value" ...>. The fragment URLs then would be "...someSegX-FragY?name=value". Ideally, there should be a command-line switch for controlling this behavior, because I can easily imagine a situation where the segment and fragment numbers are passed via the query string, e.g. <media url="some?name=value&frag=" -> "...some?name=value&frag=SegX-FragY".
don't overwrite manifest entries with same bitrate (nbcolympics.com)

Fixes #34
minor cosmetic cleanup
display first available fragment

Fixes #32