termcap: add italics and tmux entries

- add "ecma+italics" cap
- use it in "xterm-basic"
- add "tmux"/"tmux-256color" caps, fixing "so" and "se" caps,
  and sourcing "ecma+italics" and "screen"/"screen-256color"

Reviewed by:	bapt
Differential revision:	https://reviews.freebsd.org/D18363

share/termcap/termcap

@@ -2787,6 +2787,17 @@ SW|screen-w|VT 100/ANSI X3.64 virtual terminal with 132 cols:\
 screen-256color|VT 100/ANSI X3.64 terminal with 256 colors:\
 	:Co#256:pa#32767:\
 	:AB=\E[48;5;%dm:AF=\E[38;5;%dm:tc=screen:
+
+ecma+italics|ECMA-48 italics:\
+	:ZH=\E[3m:ZR=\E[23m:
+
+tmux|tmux terminal multiplexer:\
+	:so=\E[7m:se=\E[27m:\
+	:tc=ecma+italics:tc=screen:
+tmux-256color|tmux with 256 colors:\
+	:so=\E[7m:se=\E[27m:\
+	:tc=ecma+italics:tc=screen-256color:
+
 # $XTermId: termcap,v 1.78 2009/11/09 00:24:26 tom Exp $
 #
 # Note:
@@ -2829,7 +2840,8 @@ xterm-basic|modern xterm common:\
 	:me=\E[m:ml=\El:mr=\E[7m:mu=\Em:nd=\E[C:op=\E[39;49m:\
 	:rc=\E8:rs=\E[!p\E[?3;4l\E[4l\E>:sc=\E7:se=\E[27m:sf=^J:\
 	:so=\E[7m:sr=\EM:st=\EH:\
-	:ue=\E[24m:up=\E[A:us=\E[4m:ve=\E[?12l\E[?25h:vi=\E[?25l:vs=\E[?12;25h:
+	:ue=\E[24m:up=\E[A:us=\E[4m:ve=\E[?12l\E[?25h:vi=\E[?25l:vs=\E[?12;25h:\
+	:tc=ecma+italics:
 
 # The xterm-new description has all of the features, but is not completely
 # compatible with vt220.  If you are using a Sun or PC keyboard, set the