[PATCH] use realpath in templates_c/ and cache/

Hello, the attached patch adds the capability to use several template directories together with one single compile and cache dir. This is done by using the realpath to the template file instead of crc32 as a compile/cache key. The patch adds a new, readily documented option to smarty, $use_realpath, that is set to FALSE by default. Setting this to TRUE will result in the described behaviour. This works also with $use_sub_dirs set to FALSE, albeit this is not recommended because it results in very long filenames. I know there was discussion before whether this behaviour should be added to Smarty and Messju said no because it would slow down performance (http://marc.theaimsgroup.com/?l=smarty-dev&m=106867297300354&w=2). Well, for one I think this performance decrease is neglectible and since this is configurable now one can just leave it off. This patch is also helpful if you need to find compiled and cached files quickly for debugging templates. I hope this patch can be added. The patch is against current CVS development version. Hans