Add xbps_fetch_set_cache_connection() to set libfetch's cache connection limits.

Use it in xbps_fetch_file(), by default set with 8 and 16.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20100124144829-hqsr2bl6uflf0nhu

include/xbps_api.h

@@ -234,6 +234,14 @@ int xbps_fetch_file(const char *uri,
 		    bool refetch,
 		    const char *flags);
 
+/**
+ * Sets the libfetch's cache connection limits.
+ *
+ * @param[in] global Number of global cached connections, by default 8.
+ * @param[in] per_host Number of per host cached connections, by default 16.
+ */
+void xbps_fetch_set_cache_connection(int global, int per_host);
+
 /**
  * Returns last error string reported by xbps_fetch_file().
  *