This bugs clarifies a warning message issued when the query cache data
size becomes smaller than the minium allowed size.



mysql-test/r/query_cache.result:
  New warning message when a too small value has been set for query cache
  size.
sql/set_var.cc:
  To avoid poluting the QC API the warning messages are moved into the 
  QC module.
sql/share/errmsg.txt:
  Changed error message so that minimal cache size always is hinted.
sql/sql_cache.cc:
  Modified the warning message so that the minimal cache size always is
  hinted.
      
  Added interface method Query_cache::get_minimal_size_limit().
sql/sql_cache.h:
  Modified the warning message so that the minimal cache size always is
  hinted.
      
  Added interface method Query_cache::get_minimal_size_limit().