lex bugs

[utzoo!henry]

The following are locally-discovered bugs in lex:

1. The minimal lex program, "%%", which supposedly copies input to
	output, in fact exits immediately.

2. Lex is weak on syntax checking.  In particular, a null action does
	strange things and is not diagnosed.  The example in the Bell
	manual page contains a null action that should be a semicolon.

3. Ratfor output has been essentially abandoned, as is documented in the
	machine-readable lex manual but *not* in the printed V7 manual.

4. The lex library, which should be named libl.a, is in fact named
	libln.a .  Its sources are in the lex source directory, and the
	makefile there builds it properly.