utils: plaintext detection of password hash
utils: plaintext detection of password hash

* The decision to salt when verifying existing passwords should not
  depend on the current value of SECURITY_PASSWORD_HASH, as that may
  have changed since the password was stored.  (closes #272)

Co-authored-by: Brian Helba <427b8c40a6f83e2cef6522764429231629d258b5@kitware.com>

fmerges/flask-security,mafrosis/flask-security,themylogin/flask-security,nfvs/flask-security,inveniosoftware/flask-security-fork,nfvs/flask-security,fmerges/flask-security,mattupstate/flask-security,inveniosoftware/flask-security-fork,themylogin/flask-security,fuhrysteve/flask-security,inveniosoftware/flask-security-fork,fuhrysteve/flask-security,mattupstate/flask-security,mafrosis/flask-security