[NEW] Support different version types for updates.

- Available version types: releases, pre-releases (alpha, beta), nightly development builds
- Use user-set preferences to determine which version type updates to except
- If not preferences are set, determine version type by looking at the currently installed version.
Merge branch 'dev' of https://github.com/GPGTools/MacGPG2 into dev
[NEW] Update MacGPG2 to version 2.0.20 of gnupg.

- Change gnupg source location to version 2.0.20
- Add a small patch which fixes a typo in the official 2.0.20 gnupg source code.
- Adapt our own necessary patches for IDEA
- Remove CVE-2012-6085-vulnerability.patch which is now directly included in 2.0.20
- Zlib 1.2.7 download is no longer available, so update to 1.2.8
Sparkle updated.
Version set to 2.0.20
comment GPGTools - https://gpgtools.org
[FIX] Prevent pinentry keychainaccess message.

https://gpgtools.lighthouseapp.com/projects/65764/tickets/532
Log state of CODE_SIGN.
pinentry checkout bug fixed.
[FIX] Make sure scdaemon is installed again.
[FIX] Use and display correct config paths. [#106 state:fixed]
[FIX] Make sure scdaemon can find the PS/SC access module. [#106 state:fixed]
make install
[FIX] Make sure pinentry can always be launched by killing gpg-agent on logout

- shutdown-gpg-agent which is started when the user logs in and sleep
  during the entire time, till a user logs out. When they log out, it kills
  an existing instance of gpg-agent.
- shutdown-gpg-agent plist is symlinked into each user account, since it
  has to reside in ~/Library/LaunchAgents, otherwise it's not informed
  of a logout.
Merge branch 'dev' of https://github.com/GPGTools/MacGPG2 into dev
Readme updated.
Install the gpg-agent shutdown helper only in /Library/LaunchAgents.
Unload shutdown gpg-agent helper as root and as user.
build pinentry before macgpg2
Installer improved