* modules/filters/mod_proxy_html.c: Fix various code style issues.

* Use apr_is* ctype macro wrappers.

Backport of r1200556 from trunk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1238699 13f79535-47bb-0310-9956-ffa450edef68