Fixes #4446: a syntax error that happens if something else (such as
<iomanip> or <locale> in certain libstdc++ versions) includes
<libintl.h> later, which contains a function declaration for gettext
that gets mangled by the macro.
See the added comment in gettext.h and the discussion in #4446/#4452
for details.
Everywhere where wstrgettext was used, its output was converted back
to utf8. As wstrgettext internally converts the return value
from utf8 to wstring, it has been a waste. Remove the function, and
use strgettext instead.
Use wide_to_utf8 and utf8_to_wide instead of wide_to_narrow and narrow_to_wide at almost all places.
Only exceptions: test functions for narrow conversion, and chat, which is done in a separate commit.
Two new configuration options are added:
- "enable_ipv6" to enable/disable the overall use of IPv6
- "ipv6_server" to enable/disable the use of IPv6 sockets when running
a server (when "enable_ipv6" is enabled)
Now the user-level option is called ENABLE_GETTEXT, and USE_GETTEXT is
only set to true if gettext was enabled and found. This simplifies all
check to USE_GETTEXT only rather than the double checks for it being
enabled and found.
