win32: Don't include gstcollectpads.c twice

https://bugzilla.gnome.org/show_bug.cgi?id=701603
gst-launch: Improve GstContext handling

https://bugzilla.gnome.org/show_bug.cgi?id=700967
gst-launch: Remove unref that should not be there

We keep a reference to the context around all the time.

https://bugzilla.gnome.org/show_bug.cgi?id=701985
gst-uninstalled: add uridownloader lib in -bad to search paths

Even if it might not be around for long.
gst: Don't intercept --help in gst_init()

Before this patch gst_init would intercept --help, causing for example
cheese's --help to look like this:

[hans@shalem cheese]$ cheese --help
Usage:
  cheese [OPTION...] - GStreamer initialization

Help Options:
  -h, --help                        Show help options
  --help-all                        Show all help options
  --help-gst                        Show GStreamer Options

gst_init is the only gfoo_init function which does this.

https://bugzilla.gnome.org/show_bug.cgi?id=702089
structure: Add gst_structure_new_from_string()

Convenience API for bindings, gst_structure_from_string() returns
a tuple (structure, end_ptr) in bindings and is unintuitive to use
because of that.