tmux: sgr makes standout==italic

[Roman Kagan]

tmux redefines smso/rmso caps to compensate for the lack of inverse mode
in screen.

However, sgr is still inherited from screen.

As a result, setting standout mode via sgr (e.g. using ncurses'
standout()) makes the output italic rather than inverse.

This patch makes tmux' sgr a copy of screen's, but with p1 code changed
from 3 (italic) to 7 (inverse).

--- a/misc/terminfo.src 2017-11-11 23:24:40.000000000 +0300
+++ b/misc/terminfo.src 2017-11-14 12:42:18.084754388 +0300
@@ -6660,6 +6660,8 @@
 # tmux is compatible with screen, but has support for italics, and some of the
 # xterm cursor bits.
 tmux|tmux terminal multiplexer,
+       sgr=\E[0%?%p6%t;1%;%?%p1%t;7%;%?%p2%t;4%;%?%p3%t;7%;%?%p4%t;
+           5%;%?%p5%t;2%;m%?%p9%t\016%e\017%;,
        rmso=\E[27m, smso=\E[7m, use=ecma+italics,
        use=ecma+strikeout, use=xterm+edit, use=xterm+pcfkeys,
        use=xterm+sl, use=xterm+tmux, use=screen,