Include GnuPG 2.1

GnuPG is now included from the official binary package.

• configure.ac: mark gnupg-w32 as binsrc package. No longer configure gnupgs version.
• m4/gpg4win.m4: Allow packages to be .exe files.
• packages/packages.current (gnupg2): Removed. (gnupg-w32): New. (gpgme): Update to 1.6.0
• po/potfiles.in: Change gnupg2 to gnupg-w32
• po: Automated update.
• src/Makefile.am (EXTRA_DIST): Change gnupg2 to gnupg-w32 (gpg4win_bpkgs): Add gnupg-w32
• src/config.nsi.in: Change gnupg2 to gnupg-w32
• src/gpg4win.mk.in (DEFLATE_macro): Add ".exe" handling.
• src/inst-gnupg2.nsi, src/uninst-gnupg2.nsi: Removed.
• src/inst-sections.nsi: Update sections accordingly.
• src/installer.nsi (PrintCloseOtherApps): Remove checks for gpg stuff.
• src/inst-gnupg-w32.nsi, src/uninst-gnupg-w32.nsi: New.

The idea behind this change is that there is only one "core"
gnupg package and that we rely on that package.

gnupg-w32 is treated like a binary package and executed during
installation to install gnupg.

This is work in progress.