Fix displaying of long lines by explore mode

When line wrapping is off.

This is done by using recently added read_line() function.
Fix displaying of long lines by explore mode

Such lines used to be wrapped.

This is done by using recently added read_line() function.
Fix using of extra memory for some menu items

Particularly for those, that are read from other program's output.
Because of expanding horizontal tabulation and incorrect loop for
calculationg number of tabulation characters in the string, each
line used to get reserved (len*(cfg.tab_stop - 1) + 1) bytes
instead of (len + ntabs(cfg.tab_stop - 1) + 1).
Remove unused field of the status_t structure

The field was called "search" and probably served as a global flag
to designate search availability.
Replace manual loop with memset()

This should be both faster and easier to read and understand.
Move tabulation expansion to a separate function
Move and improve get_first_wchar() to utils/stra.c

Used to be resident of modes/normal.c.
Move common code for expanding tabs to utils/str.c
Merge branch 'fix-long-lines-read'