Escape story fields and clean story HTML with HTML Purifier.

Add HTML Purifier 4.19.1. Stories are purified when they are saved and
when they are shown.

lib/htmlpurifier-4.19.1/library/HTMLPurifier/ConfigSchema/schema/Attr.DefaultImageAlt.txt

@@ -0,0 +1,11 @@
+Attr.DefaultImageAlt
+TYPE: string/null
+DEFAULT: null
+VERSION: 3.2.0
+--DESCRIPTION--
+This is the content of the alt tag of an image if the user had not
+previously specified an alt attribute.  This applies to all images without
+a valid alt attribute, as opposed to %Attr.DefaultInvalidImageAlt, which
+only applies to invalid images, and overrides in the case of an invalid image.
+Default behavior with null is to use the basename of the src tag for the alt.
+--# vim: et sw=4 sts=4