Fix constant time comparison

	modified:   lib/App/bmkpasswd.pm
	new file:   t/00_comparison.t
test / POD tweaks

	modified:   lib/App/bmkpasswd.pm
	modified:   t/00_comparison.t
	modified:   t/01_md5.t
	modified:   t/02_bcrypt.t
	modified:   t/03_sha.t
	modified:   t/04_hashopts.t
const time comparison function can return early if length mismatch

	modified:   lib/App/bmkpasswd.pm
v2.005001

  - SECURITY; passwdcmp() constant time comparison fixes.

    The last character of a hash can be skipped during constant time
    comparison in previous versions (starting at 1.83).

    Real-world risk is reasonably low, but this does make collisions more
    likely. Mea culpa.

  - POD / test expansion