Fix for extra newline that gets appended if a command is not found in
the new parser
Remove support for invoking old pager
Remove old fish_pager source and implementation
Remove old pager remnants, including documentation and references in the
build system
Remove support for input IO_BUFFERs, which were only used by fish_pager
Fix for issue where pager contents may stay around if you executed a
command with pager contents visible
Check for libtinfo after libncurses

See Gentoo bug 459768 (https://bugs.gentoo.org/show_bug.cgi?id=459768)

Closes #1322 (https://github.com/fish-shell/fish-shell/pull/1322).