tui: Add terminfo patches for linux on MacOS.

Also enable italics on Konsole when it is falsely claiming to be xterm.
Also note the reasons for some of the patcher terminfo patches.

src/nvim/tui/tui.c

@@ -1214,6 +1214,9 @@ static void patch_terminfo_bugs(TUIData *data, const char *term,
 {
   unibi_term *ut = data->ut;
   const char * xterm_version = os_getenv("XTERM_VERSION");
+#if 0   // We don't need to identify this specifically, for now.
+  bool roxterm = !!os_getenv("ROXTERM_ID");
+#endif
   bool xterm = terminfo_is_term_family(term, "xterm");
   bool linuxvt = terminfo_is_term_family(term, "linux");
   bool rxvt = terminfo_is_term_family(term, "rxvt");
@@ -1227,6 +1230,7 @@ static void patch_terminfo_bugs(TUIData *data, const char *term,
     || terminfo_is_term_family(term, "iTerm.app");
   // None of the following work over SSH; see :help TERM .
   bool iterm_pretending_xterm = xterm && iterm_env;
+  bool konsole_pretending_xterm = xterm && konsole;
   bool gnome_pretending_xterm = xterm && colorterm
     && strstr(colorterm, "gnome-terminal");
   bool mate_pretending_xterm = xterm && colorterm
@@ -1260,25 +1264,37 @@ static void patch_terminfo_bugs(TUIData *data, const char *term,
     // their own terminal types and terminfo entries, like PuTTY does, and not
     // claim to be xterm.  Or they would mimic xterm properly enough to be
     // treatable as xterm.
-#if 0   // We don't need to identify this specifically, for now.
+
-    bool roxterm = !!os_getenv("ROXTERM_ID");
+    // 2017-04 terminfo.src lacks these.  genuine Xterm has them, as have
-#endif
+    // the false claimants.
     unibi_set_if_empty(ut, unibi_to_status_line, "\x1b]0;");
     unibi_set_if_empty(ut, unibi_from_status_line, "\x07");
     unibi_set_if_empty(ut, unibi_set_tb_margin, "\x1b[%i%p1%d;%p2%dr");
+
     if (true_xterm) {
+      // 2017-04 terminfo.src lacks these.  genuine Xterm has them.
       unibi_set_if_empty(ut, unibi_set_lr_margin, "\x1b[%i%p1%d;%p2%ds");
       unibi_set_if_empty(ut, unibi_set_left_margin_parm, "\x1b[%i%p1%ds");
       unibi_set_if_empty(ut, unibi_set_right_margin_parm, "\x1b[%i;%p2%ds");
     }
-    if (iterm_pretending_xterm) {
+    if (true_xterm
+        || iterm_pretending_xterm
+        || gnome_pretending_xterm
+        || konsole_pretending_xterm) {
+      // Apple's outdated copy of terminfo.src for MacOS lacks these.
+      // genuine Xterm and three false claimants have them.
       unibi_set_if_empty(ut, unibi_enter_italics_mode, "\x1b[3m");
+      unibi_set_if_empty(ut, unibi_exit_italics_mode, "\x1b[23m");
     }
   } else if (rxvt) {
+    // 2017-04 terminfo.src lacks these.  Unicode rxvt has them.
     unibi_set_if_empty(ut, unibi_enter_italics_mode, "\x1b[3m");
+    unibi_set_if_empty(ut, unibi_exit_italics_mode, "\x1b[23m");
     unibi_set_if_empty(ut, unibi_to_status_line, "\x1b]2");
     unibi_set_if_empty(ut, unibi_from_status_line, "\x07");
-    unibi_set_if_empty(ut, unibi_set_tb_margin, "\x1b[%i%p1%d;%p2%dr");
+    // 2017-04 terminfo.src has older control sequences.
+    unibi_set_str(ut, unibi_enter_ca_mode, "\x1b[?1049h");
+    unibi_set_str(ut, unibi_exit_ca_mode, "\x1b[?1049l");
   } else if (screen) {
     // per the screen manual; 2017-04 terminfo.src lacks these.
     unibi_set_if_empty(ut, unibi_to_status_line, "\x1b_");
@@ -1287,14 +1303,21 @@ static void patch_terminfo_bugs(TUIData *data, const char *term,
     unibi_set_if_empty(ut, unibi_to_status_line, "\x1b_");
     unibi_set_if_empty(ut, unibi_from_status_line, "\x1b\\");
   } else if (terminfo_is_term_family(term, "interix")) {
+    // 2017-04 terminfo.src lacks this.
     unibi_set_if_empty(ut, unibi_carriage_return, "\x0d");
   } else if (linuxvt) {
-    // No bugs in the vanilla terminfo for our purposes.
+    // Apple's outdated copy of terminfo.src for MacOS lacks these.
+    unibi_set_if_empty(ut, unibi_parm_up_cursor, "\x1b[%p1%dA");
+    unibi_set_if_empty(ut, unibi_parm_down_cursor, "\x1b[%p1%dB");
+    unibi_set_if_empty(ut, unibi_parm_right_cursor, "\x1b[%p1%dC");
+    unibi_set_if_empty(ut, unibi_parm_left_cursor, "\x1b[%p1%dD");
   } else if (putty) {
     // No bugs in the vanilla terminfo for our purposes.
   } else if (iterm) {
+    // 2017-04 terminfo.src has older control sequences.
     unibi_set_str(ut, unibi_enter_ca_mode, "\x1b[?1049h");
     unibi_set_str(ut, unibi_exit_ca_mode, "\x1b[?1049l");
+    // 2017-04 terminfo.src lacks these.
     unibi_set_if_empty(ut, unibi_set_tb_margin, "\x1b[%i%p1%d;%p2%dr");
     unibi_set_if_empty(ut, unibi_orig_pair, "\x1b[39;49m");
     unibi_set_if_empty(ut, unibi_enter_dim_mode, "\x1b[2m");