Fix building on OpenSuSE Leap 42.2: gpgme master requires recent libgpg-error.

Leap 42.2 only has libgpg-error0-1.13-4.19.x86_64, while gpgme master requires
libgpg-error >= 1.17.

Compiling all this stuff also required installing more recent versions of
gettext, automake and autoconf than Leap 42.2 provides, using devel:tools:building.

I'm afraid that gpgme master will soon need more recent version of other things too
(e.g. gnupg), as things evolve, so I hope we can quickly switch to a stable
branch or release tag of gpgme instead, rather than following master.

CCMAIL: aheinecke@intevation.de