Use it for the actual I/O only. Previously, defining CONFIG_UTF8 and
enabling UTF-8 used to force many strings to the UTF-8 charset
regardless of the terminal charset option. Now, those strings always
follow the terminal charset. This fixes bug 914 which was caused
because _() returned strings in the terminal charset and functions
then assumed they were in UTF-8. This reduction in the effects of
UTF-8 I/O may also simplify future testing.
The configure script no longer recognizes "CONFIG_UTF_8=yes" lines
in custom features.conf files. They will have to be changed to
"CONFIG_UTF8=yes". This incompatibility was deemed acceptable
because no released version of ELinks supports CONFIG_UTF_8.
The --enable-utf-8 option was not renamed.
Preparation for using struct terminal in formating functions.
By now distinguish between formating widgets and formating widgets with
displaying was done with term == NULL and term != NULL. I hope I'am
not wrong.
