Merge remote branch 'upstream/stable-0.15' into stable-0.15

Merge remote branch 'upstream/stable-0.15' into stable-0.15

* upstream/stable-0.15:
  Version 0.15.1
  qed: fix use-after-free during l2 cache commit
  sdl: Fix termination in -no-shutdown mode
  Fix termination by signal with -no-shutdown
  Add support for finding libpng via pkg-config.
  Check for presence of compiler -pthread flag.
  Allow overriding the location of Samba's smbd.
  Fix linker scripts
  Fix install(1) usage to be compatible with OpenBSD's install(1).
  Fix qjson test of solidus encoding
  configure: Copy test data to build directory
  monitor: fix build breakage for !CONFIG_VNC
  monitor: fix build breakage with --disable-vnc
  Fix forcing multicast msgs to loopback on OpenBSD.
  user: Restore debug usage message for '-d ?' in user mode emulation

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>