Never freeze again.

Put snapshot related floaters always on top of the full screen preview.
Make having multiple running uploads more robust.
Fix infinite recursion when clicking on the bottom 'Snapshot' button
under certain conditions.
Unfreeze time more robust; unfreeze time out of precaution when
starting an upload (if 'Keep open' not checked).
Fixed a bug that caused all callbacks for successful feed uploads to be
ignored.
Merge branch 'master' into meshupload
Merge remote-tracking branch 'singu/master'
Merge branch 'master' into meshupload
Fixed a build issue in clang
Add support for ".dae" (and others) to filepicker load filter.

* Brought llfilepicker.{cpp,h} up to speed with V3 by adding
  FFLOAD_MODEL, FFLOAD_COLLADA, FFLOAD_SCRIPT, FFLOAD_DICTIONARY
  However, note that we used FFLOAD_LSL, so I renamed their
  FFLOAD_SCRIPT to FFLOAD_LSL and kept our way of filtering.
* Fixed the filter token that is sent to the plugin for
  collada (from "dae" to "collada").
Renamed FFLOAD/SAVE_LSL to FFLOAD/SAVE_SCRIPT
Fix memory leak. This auto deletes the file picker, the old code did't.
Fix crash because of missing debug setting
Fixed mesh file picker and then some
Remove FloaterModelPreviewRect
v-d llviewermenufile.cpp functions (and order) for meshupload, decide when Upload Mesh entry should be enabled.
Merge branch 'master' into meshupload
Merge remote-tracking branch 'Aleric/meshupload' into meshupload
Merge remote-tracking branch 'Lirusaito/meshupload' into meshupload
Build fixes