Update slowfs_cache third-party module from 1.6 to 1.7.
Do not bump PORTREVISION because this module disabled by default.
2012-02-28 VERSION 1.7
* Fix on-disk cache size calculation.
Since the initial release, recorded on-disk cache size was
decreased twice for purged content (once during cache purge
and once during subsequent cache update).
This resulted in recorded on-disk cache size being much
smaller than in reality, which could lead to on-disk cache
outgrowing defined "max_size" parameter.
Patch from Pyry Hakulinen (via ngx_cache_purge, months ago).
* Append path of the file being cached to the slowfs process