Reorganize string buffers.
Global buffers used to have descriptive names, but as the need to
more temporary buffer appears we have to decide between creating
new global buffers or reusing existing ones disregarding their
names. Therefore, to avoid the creation of too many buffers or the
use of confusing variable names, this change give more generic
names to buffers, except for INPUT, which is only used for input.
The wide buffer has been made into a global buffer.
All global string buffers now have the same size, BUFLEN.