Add a beta build configuration, and use it for betas. Change beta, debug, and nightly build configurations to set the preprocessor BETA=1. Add ITBetaAssert, which crashes only in those build configurations. Add some ITBetaAsserts to find why we sometimes try to get negative line numbers.

It didn't work because sparkle uses its own version comparator to detect downgrade attacks.

This reverts commit 512c5b4a.

Change the version number to 3.1.x. This affects only nightly builds, which will be named 3.1.x-nightly. When I build a beta release, the release_beta script will tack on .beta, so it must be run as release_beta.sh 3.1.0. That will produce 3.0.1.beta. This commit adds a Sparkle version comparator that special-cases versions ending in .beta so that a non-beta with the same first two parts will compare as newer (e.g., 3.1 is newer than 3.1.9.beta).

Modify release_beta to modify experiment files (testing3 and testing_changes3) so it's easy to roll changes out gradually to the population

Merge in code from hotkeyWindowsInPanels branch. Support multiple hotkey windows. Update the shortcut input view. Add support for floating panel terminal windows.

Rename release.sh to release_beta.sh. It is for releasing widely-deployed beta builds. release3.sh is for the early adopters.