grow_fd() sets errno/errstr

Note the use of error(current_errstr()).  grow_fd() already set errstr,
but we still wanted to do the error longjmp.  Using current_errstr()
should maintain the previous errstr.  It's a format print, again, from
current_errstr into current_errstr again.

Since this commit messed with one of the Ebadf's, I knocked out the
other too.  The long term goal is to not use any of the hardcoded
errstrs (preferring errno for that).  This's one more hardcoded errstr
string removed, with 67 to go!