Update to 2.1.21, which in particular fixes a keyring corruption bug.

• gpg,gpgsm: Fix corruption of old style keyring.gpg files. This bug was introduced with version 2.1.20. Note that the default pubring.kbx format was not affected.
• gpg,dirmngr: Removed the skeleton config file support. The system's standard methods for providing default configuration files should be used instead.
• w32: The Windows installer now allows installion of GnuPG without Administrator permissions.
• gpg: Fixed import filter property match bug.
• scd: Removed Linux support for Cardman 4040 PCMCIA reader.
• scd: Fixed some corner case bugs in resume/suspend handling.
• Many minor bug fixes and code cleanup.

MFH: 2017Q2