gnu-pw-mgr: Update to 2.7.4

* Use pkgsrc libtool.
* Use MASTER_SITE_GNU as MASTER_SITES.

Changelog:
New in 2.7.4 - September 2020
New in 2.4 - August, 2018

disable the --use-pbkdf2 option and implement --rehash as replacement

* the default "rehash" count is printed with --status output
* security question answers can now be stable across password
  changes. Two answers are now printed: the deprecated version
  that changes with the rehash count, and the new version that
  is stable.

New in 2.2 - June, 2018

* Chase Bank has added the password restriction that no three characters
  may be in sequence. So look for that and fix it, if need be.

* Let people know when they last modified a password.
  Mark the day when the pbkdf2 count is modified.

* The confirmation value printed out is a hash based on the confirmation
  string and the current password. So, if the password changes, then
  so does the confirmation string. Not ideal. This change restricts
  the hashing source to just the password id and the confirmation
  string.

* Users may now specify a config file other than the default.

New in 2.0 - May, 2016

* A new option --shared to implement sharing passwords.
  This allows shared logins with secure passwords and still
  keeps all the other passwords very secret.  See the docs for
  the rationale and usage.


(ryoon)