Use modern gettext implementation from libgpg-error.
* src/w32-gettext.c, src/w32-gettext.h: Remove * src/Makefile.am (gpgex_SOURCES): Remove above files. * configure.ac (AH_BOTTOM): Define GPG_ERR_ENABLE_GETTEXT_MACROS. * src/main.h: Include gpg-error.h. (gettext_noop): Move from w32-gettext.h. * src/main.cc (get_locale_dir): Replace by code taken from libgpg-error. (i18n_init): Remove setlocale calls.