Use the stable Condvar API

[dvdplm]

Switch to use wait_while and wait_timeout_while as the outcome of
rust-lang/rust#67076 removed wait_until and
wait_timeout_until. Switches the predicate logic around.

[rjwalters]

Thanks for this contribution! For the time being, we are using the nightly-2019-12-19 rust toolchain so the new Condvar interface is not available to us yet. This decision is driven by recent changes in 32 bit iOS support in rust-lang and our desire to support SDK development on older iPhones, like the iPhone 5. This PR will likely have to wait until we drop support for these older devices.

[dvdplm]

Ah, that was the missing piece of info, thank you for that. Feel free to close or leave it open until the time comes, as you prefer. :)

[rjwalters]

@dvdplm - my attempt to rebase your PR resulted in it being closed... we actually just updated our rust toolchain so I was attempting to get your patch ready to merge. Perhaps you can reopen it?

[eranrund]

@rjwalters The changes here were already implemented by @jcape in #264

[rjwalters]

@rjwalters The changes here were already implemented by @jcape in #264

perhaps that's why it ended up closing the PR?

Thanks again @dvdplm for contributing to the project!