QUERY CACHE - low memory cleanup method

instead of removing queries from cache with today method, we could create a new method (news methods)

query_cache_clean_method=DEFAULT / PROCEDURE

DEFAULT is today implementation

PROCEDURE will execute some mysql schema stored procedure

since query cache can be veeery big (today i'm using 100MB), maybe procedure will lock query cache a lot, and queries will not hit query cache...
well in this case we could continue with query cache locked, or timeout and get back to default method

add a new global variable: query_cache_clean_timeout= 999999 in seconds, if set to "0" don't timeout

well that's just an idea =) query cache is a nice feature, and, yes, it's not the main function of database / application development/runtime, but it can speed up many things very easly, in other words, a good cache (with very high hit rate) is a performace boost in any system

in coments i will put some ideas from others MDEV (sorry about many comments in others MDEV), that could be procedures or method to remove queries from cache when lowmem