Separate number of lines to sync from tmux integration from number of lines of history to keep

Thanks for filing an issue! Please answer the questions below so I can help you.

• iTerm2 version: Build 3.0.15
• OS version: MacOS Sierra 10.12.4
• Attach ~/Library/Preferences/com.googlecode.iterm2.plist here (drag-drop from finder into this window)
• Attach a debug log, if possible. Instructions at https://iterm2.com/debuglog
• Are you reporting a performance issue or a hang? Please attach a sample. Instructions at https://gitlab.com/gnachman/iterm2/wikis/HowToSample
• Are you reporting a crash? Please attach the crash log. Instructions at https://gitlab.com/gnachman/iterm2/wikis/crash-logs

Detailed steps to reproduce the problem:

1. Open a tmux integration session in iterm
2. Run a command that produces >1000 lines of output
3. Attempt to scrollback

What happened: Scrollback is cut off at 1000 lines of output, even though I have unlimited scrollback in iterm plist and tmux.conf.

What should have happened: Scrollback should be unlimited.