ffmpeg: drop 2.6 & 2.7, bump to 2.8.7 & 3.0.2, minor fixes. (WIP) (#579)

* Drop 2.6.3 & 2.7.2, bump 2.8.6 to 2.8.7 and 3.0.1 to 3.0.2.
* ffmpeg, ffprobe and ffserver were being shipped in secondary arch
  builds (due to rm $binDir instead of rm $prefix/bin where they were
  being installed) but did not have a cmd: in PROVIDES. Fixed this by
  moving these to a _bin subpackage on x86_gcc2 using 2nd arch x86.
* Fix CONFLICTS_devel in 3.0.2 (missing "_legacy"),
* Add ffmpeg2_bin to CONFLICTS in 3.0.2.
* Add ffmpeg and ffmpeg_legacy to CONFLICTS_bin in 2.8.7.
* Reorder some sections.
* Switch all HOMEPAGE and SOURCE_URI to https.
* Switch from tar.bz2 to tar.xz for 2.8.7.
* 2.8.7 and 3.0.2 build OK (on x86_gcc2 using x86 as 2nd arch) but
  "make check" fails with "runtime_loader: Cannot open file
  libavutil.so.55: No such file or directory". Failure happens on
  TEST api-threadmessage for 3.0.2 and on TEST api-flac for 2.8.7.

media-video/ffmpeg/patches/ffmpeg-2.8.7.patchset

@@ -8,7 +8,7 @@ diff --git a/configure b/configure
 index 475c087..5a95b97 100755
 --- a/configure
 +++ b/configure
-@@ -6052,6 +6052,7 @@ enabled threads && ! enabled pthreads && ! enabled atomics_native && die "non pt
+@@ -5783,6 +5783,7 @@ enabled threads && ! enabled pthreads && ! enabled atomics_native && die "non pt
  if test $target_os = "haiku"; then
      disable memalign
      disable posix_memalign

media-video/ffmpeg/patches/ffmpeg-3.0.2.patchset

@@ -8,7 +8,7 @@ diff --git a/configure b/configure
 index 475c087..5a95b97 100755
 --- a/configure
 +++ b/configure
-@@ -6052,6 +6052,7 @@ enabled threads && ! enabled pthreads && ! enabled atomics_native && die "non pt
+@@ -6040,6 +6040,7 @@ enabled threads && ! enabled pthreads && ! enabled atomics_native && die "non pt
  if test $target_os = "haiku"; then
      disable memalign
      disable posix_memalign