smoothstreamingenc: Write to a temp file while updating the manifest

If a client tries to read the file while it's being updated, the client
would get an incomplete manifest. Instead write to a separate temp file
and atomically rename it to replace the previous one.

Signed-off-by: Martin Storsjö <martin@martin.st>
w32threads: Don't use function pointers when linking directly to newer APIs

This reduces the call overhead slightly. More noticeably, it
restores the earlier (unintended?) feature that condition variable
functions work just fine even if w32thread_init() hasn't been called.
This was broken as a side effect of 4622f11f9, if explicitly targeting
Vista+.

This makes w32threading work in VP8 again, if targeting Vista+.

Signed-off-by: Martin Storsjö <martin@martin.st>
Revert "w32pthread: help compiler figure out undeeded code"

This reverts commit 4622f11f9c83db8a2e08408c71ff901826ca652c.

The compiler should be able to do the dead code elimination now
without this when the cond_* names point directly to the real
functions instead of to local function pointers.

Signed-off-by: Martin Storsjö <martin@martin.st>