Add --absolute flag

This allows a user to set a full path without getting a .keychain suffix
automatically appended.
Add support for the --query option

To work with systemd, just the environment variables should be printed.
To support this, --query now removes any shell boilerplate related to
exporting the variables.
Add support for injecting agents into systemd
Fix rpm spec
Write ~/.gpg-agent-info when launching gpg-agent...

... for better compatibility with other things using it, e.g. KDE 4:
see: https://bugzilla.redhat.com/show_bug.cgi?id=486025

Patch from: Ville Skyttä