Need a cache for ucnv_open()

A number of extensions/functions (strangely, most of the things I work on :-) will need to be able to convert between unicode and arbitrary encodings. It makes a lot of sense to keep some kind of per-request cache (of limited length) to avoid having to load and unload the conversion table on each conversion attempt. Since this cache needs to always be present (to avoid crazy conditional compilation) we either need to put it in zend_unicode.c or put it in ext/unicode and always require it to be statically compiled into php. Thoughts? --Wez.