streamsynchronizer: Set proxy flags on the pads and use default event handler for simplicity

https://bugzilla.gnome.org//show_bug.cgi?id=705555
videodecoder: Clear taglist on reception of a STREAM_START event

https://bugzilla.gnome.org/show_bug.cgi?id=705109
audiodecoder: Clear taglist on reception of a STREAM_START event

https://bugzilla.gnome.org/show_bug.cgi?id=705109
gio: make better use of the cached buffer

When playing mp3 files from a smb server, we get 64k read requests
that mostly overlap.  Without using the cache to partially satisfy
these, we send these requests straight to the server, resulting in
a lot more network traffic than necessary.

https://bugzilla.gnome.org/show_bug.cgi?id=705415
typefind: Add typefind function for WebP image format

https://bugzilla.gnome.org/show_bug.cgi?id=705826
playbin-complex: Set fakesink as audio-sink to not use a real audio device

https://bugzilla.gnome.org/show_bug.cgi?id=705157
.gitignore: Ignore files from automake test-driver
check: Update .gitignore
discoverer: document that "finished" and "discovered" signals are only emitted in async mode

https://bugzilla.gnome.org/show_bug.cgi?id=660195
gio: fix printf format compiler warning
playsink: Don't set sink to NULL if a new one is set while the old one is still in use
typefind: ADTS/AAC, find more aac sync to select correctly

https://bugzilla.gnome.org/show_bug.cgi?id=691462
video{en,de}coder: Revert to old ::reset() behaviour and deprecate it
video{en,de}coder: Add new flush vfunc as a replacement for reset
videodecoder: Don't reset decoder on segment events

Either there was a flush before that resets everything anyway,
or resetting would make us lose information we might need if
it's just a segment update.
theora: Use new video codec base classes' flush vfunc
videodecoder: Don't reset too much if we're resetting because of a soft-flush

Fixes reverse playback with Ogg/Theora.
typefind: improved and extended typefinder for module music formats

introduced new caps: audio/x-mod, modtype : { xm, okt, mod, ptm, ... }

https://bugzilla.gnome.org/show_bug.cgi?id=706061
Revert "typefind: improved and extended typefinder for module music formats"

This reverts commit 4c79f35c7abc78bf4d325a8cd2059e8832ea0b34.

It causes some MP4 files to be detected as mod files.
tests: add test-header-compile script

https://bugzilla.gnome.org/show_bug.cgi?id=695889