Add "check for updates" to menubar icon

Disable tabbing completely. The user defaults hack isn't sufficient because holding down option causes a new window to open as a tab. Issue 6197

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.

Prevent calls to retainWindow:withTab with a nil tab, which apparently happens although I don't know how or why. There was a crash log.

Remove some weird logic dating back to commit ee11b549068742112b4d7e3141a9eeece81aa50f in the old-iterm repo that was supposed to "improve function key handling" and made Fn+Ctrl+key send the key ignoring modifiers and Fn+key (without Ctrl) send the key with modifiers, as though Fn weren't pressed. I have no idea what this was meant to do but it caused issue 6176

Reset user scroll when the buffer is cleared. Change the convenience accessor for verticalScroller to ptyVerticalScroller since in xcode 9 you can no longer override a superclass method and change the return type to a subclass of the method's original return type. Issue 6174

Add iTermCallWithTimeout since 10.13 has a lot of system calls that never return. Prevent proc_pidinfo for hanging for more than half a second.

Update colorpicker to use latest project settings and warnings. Fix a bug where the eyedropper window is never hidden on 10.13. Issue 6171

When the autocomplete window opens and then discovers it has no results and closes it causes a nonpinned hotkey window to close because the window gets closed before becoming key. That confuses the very complex logic for autohiding. To make the smallest possible change, I do a dispatch async on the close to order it properly. Issue 6169.

Prevent statfs from hanging the app for more than half a second in the face of broken network filesystems. Issue 6110

Don't set desiredRows_/desiredColumns_ when adding a tab to an existing window. It should stay at the value set by the first tab. Issue 6141.

Fix warnings introduced in Xcode 9

Fix vertical alignment of 'Paste' button in advanced paste.

actually allows this if screens don't have their own spaces. Issue 6125

This fixes both deadkeys alone (e.g., ` on a DE keyboard) or deadkey+key (opt+` on DE to give '). I tested migration from 3.0 and it seems fine.

If no local authentication policy can succeed, then authenticate the password manager. This is the previous behavior from 3.1.1. Apparently OS X 10.11 has the APIs but can't authenticate with them. Issue 6113

Disable High Sierra's system tabs, which you can get when System Prefs > Docks > Prefer tabs when opening documents is set to Always. Issue 6096