Update to 5.92

Upstream changes:
5.92  Sun Jun  1 00:15:44 MST 2014
- fixed reserved-word clash when compiling with C++
-- use 'classname' instead of 'class'
-- ref. SHA.xs (rt.cpan.org #96090)
- silenced MSC compiler warning about signed/unsigned comparison
-- ref. SHA.xs (rt.cpan.org #95830)

5.91  Fri May 16 10:21:44 MST 2014
- restored original 'addfile' for use on opened file handles
-- allows callbacks in place of actual files
-- ref. IO::Callback (rt.cpan.org #95643)
- re-established inheritance from Digest::base
-- to pick up future Digest enhancements automatically
- cleaned up documentation

5.90  Wed May  7 07:57:08 MST 2014
- consolidated all dynamic memory allocation into XSUBs
-- streamlines referencing of SHA objects
-- simplifies DESTROYing of objects
- enhanced Makefile.PL to allow 'use warnings'
-- automatically reverts to $^W for early Perls
- scrubbed C and Perl code to remove all compiler warnings

(wen)