Optimized django.utils.text.capfirst().

Unconditionally coercing to str type twice is expensive.

django/utils/text.py

@@ -12,7 +12,11 @@ from django.utils.translation import gettext as _, gettext_lazy, pgettext
 @keep_lazy_text
 def capfirst(x):
     """Capitalize the first letter of a string."""
-    return x and str(x)[0].upper() + str(x)[1:]
+    if not x:
+        return x
+    if not isinstance(x, str):
+        x = str(x)
+    return x[0].upper() + x[1:]
 
 
 # Set up regular expressions