patch 8.0.1833: X11: ":echo 3.14" gives E806

Problem:    X11: ":echo 3.14" gives E806.
Solution:   set LC_NUMERIC to "C". (Dominique Pelle, closes #2368)

src/gui_x11.c

@@ -1282,6 +1282,17 @@ gui_mch_init_check(void)
 		cmdline_options, XtNumber(cmdline_options),
 		CARDINAL &gui_argc, gui_argv);
 
+# if defined(FEAT_FLOAT) && defined(LC_NUMERIC)
+    {
+	/* The call to XtOpenDisplay() may have set the locale from the
+	 * environment. Set LC_NUMERIC to "C" to make sure that strtod() uses a
+	 * decimal point, not a comma. */
+	char *p = setlocale(LC_NUMERIC, NULL);
+
+	if (p == NULL || strcmp(p, "C") != 0)
+	   setlocale(LC_NUMERIC, "C");
+    }
+# endif
     if (app_context == NULL || gui.dpy == NULL)
     {
 	gui.dying = TRUE;

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1833,
 /**/
     1832,
 /**/