input() is used to accept filenames when saving, regular
expressions when searching, and other input. It writes
the characters into buffers such as file and exp_buf and
others which are of length LINE_LEN.
To prevent writing beyond the end of the intended buffer,
truncate the input at LINE_LEN - 1 and ensure that the
string is NULL terminated.
Change-Id: I142baa8cfae38bdd7fa648d86559d6d9b8e7a7fd
ef31660ff2