Fix testReferenceRemovedFromNotificationCenter to actually test what needs to be tested, even when run on 10.11.

notification center on dealloc. Do not leak _class. If the weak reference's object gets its class
changed at runtime, respect that. I believe the crash would occur when a weak reference gets
released before its object. When the object is released, it'll post a notification that is received
by a now-dealloc'ed weak reference.

this didn't always crash. Maybe it always dies on older OSes since 10.11 automatically removes the
observer.

Use the correct observer for disabling the default-bg-transparency button. The wrong one worked because reloadProfiles triggers all the observers :(. Also disable the blur-related things when transparency is off.

Add a checkbox to Window profile prefs to make non-default background colors always opaque. From pull request 277.

Draw the mark with a bezier path instead of an image. Its height scales with the line's height to make it more visible. Issue 4504, kind of.

Remove the last command mark when the current command is aborted, as happens when you resize the window at a bash prompt. Issue 4504

Remove the last command mark when the current command is aborted, as happens when you resize the window at a bash prompt. Issue 3183

Make the Secure Input menu item indicate the true state of secure input. It used to show the checkmark ooly if it was both on /and/ on because of iTerm2. Also, the way the checkmark was set was kind of weird--it should have been set in validateMenuItem:.

Change target membership of golden files to iTerm2Tests and iTerm2XCTests to try to get the files to copy on Travis.

Add separate golden images for Travis. Increase the failure threshold for golden tests to 10% brightness difference. I observed as high as 6.5% brightness diffs between two machines running the same OS, probabily attributable to different color profiles for the attached display.

Log deciles of diffs (by amount difference, where 0 is identical and 1 is black vs white) on failing golden tests. Deciles don't include exactly matching pixels.