parseGroovyFromPage does not use the target page's programming rights

It appears that using xwiki.parseGroovyFrom page in velocity to create a groovy object to work with ignores the programming rights of the groovy page.

I discovered this by using configurationSheet: the call works when using /view/ but fails when using /admin/; this is a call to `services.component.getInstance(Class.forName("org.xwiki.configuration.ConfigurationSource"), "xwikicfg")`. This can be measured with simply `services.components` which returns a script-oriented object.