Update SHA1 code to RFC 6234

Update SHA1 code to RFC 6234

RFC 6234 is an update to RFC 3174 from which the code was originally taken.
It has a slightly better code, and a better phrased license (simple 3-clause
BSD).

* main/sha1.c is sha1.c from RFC 6234 with formatting changes only.
* include/asterisk/sha1.h merges sha.h and sha-private.h from RFC 6234.
* Removed unused include of asterisk/sha1.h from main/channels.c

Review: https://reviewboard.asterisk.org/r/1503/

Merge-From: http://svn.asterisk.org/svn/asterisk/branches/1.8@340263

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@340280 65c4cc65-6c06-0410-ace0-fbb531ad65f3