Log Message:
Update thin to 1.6.3.

pkgsrc change: Add pkg_alternatives support.

== 1.6.3 Protein Powder
 * Add HTTP 422 status code [rajcybage]
 * Add warning about EM reactor still running when stopping.
 * Remove version number from "Server" HTTP header. [benbasson]
 * Adding `--ssl-disable-verify` to allow disabling of client cert requests when \ 
SSL enabled [brucek]
 * Ensure Tempfiles created by a large request are closed and deleted. [Tonkpils]