Update third-party slowfs_cache module from 1.9 to 1.10.
Do not bump PORTREVISION.
* Fix compatibility with nginx-1.1.12+.
Due to the changes in cache index usage accounting (1 per request
instead of 1 per access) initial cache insert of "small" file was
decreasing usage count, rendering index entry invalid.
Because cache manager ignores invalid entries, expired cache files
were not being removed from the cache, which forced it to outgrow
specified "max_size" value.