learn bugs

[utzoo!duke!unc!grumpy!smb]

There are a few bugs in the distributed learn:
	a) When a sub-shell is invoked by makpipe.c, its output on file 2
	   is going direct to the terminal rather than through a pipe; this
	   can cause prompts to be intermixed with other output.  Fix:  in
	   makpipe.c, in the fork that will actually invoke the shell, close
	   file 2 and dup(1).

	b) In the distributed PDP 11 version (though not in UCB VAX UNIX),
	   routine start.c uses its own structure to describe a directory;
	   this structure in turn gives the type of an i-node as "int", which
	   causes portability problems on 32-bit machines.

	c) In tee.c, a single character is read into the &i, which is an "int";
	   this value is then used as the argument to putc.  While this code
	   works properly on PDP-11s and VAXes, it fails on any machine
	   where the bytes aren't backwards.