common.cpp: check wcwidth for supported characters

Rather than trying to detect Unicode support from the environment, check
the printable width of characters in the current locale before deciding
on whether to use them.

Closes #1927.

src/common.cpp

@@ -525,13 +525,10 @@ wcstring wsetlocale(int category, const wchar_t *locale)
     /*
       Use ellipsis if on known unicode system, otherwise use $
     */
-    char *ctype = setlocale(LC_CTYPE, NULL);
-    bool unicode = (strstr(ctype, ".UTF") || strstr(ctype, ".utf"));
-
-    ellipsis_char = unicode ? L'\x2026' : L'$';
+    ellipsis_char = (wcwidth(L'\x2026') > 0) ? L'\x2026' : L'$';
 
     // U+23CE is the "return" character
-    omitted_newline_char = unicode ? L'\x23CE' : L'~';
+    omitted_newline_char = (wcwidth(L'\x23CE') > 0) ? L'\x23CE' : L'~';
 
     if (!res)
         return wcstring();

src/screen.cpp

@@ -1424,6 +1424,7 @@ void s_reset(screen_t *s, screen_reset_mode_t mode)
         wcstring abandon_line_string;
         abandon_line_string.reserve(screen_width + 32); //should be enough
 
+	/* Don't need to check for wcwidth errors; this is done when setting up omitted_newline_char in common.cpp */
         int non_space_width = wcwidth(omitted_newline_char);
         if (screen_width >= non_space_width)
         {