not implemented:
	- mode.input_allow_dollars.
	- column counts do not take tabstops into account.
	- mode.output_linenumbers.
	- mode.do_depend.
	- mode.do_macrolist.
	- mode.do_trace.
	- warns.endiflabels. (they cause errors)
	- warns.unused.	
	- the -iremap option.
	- #line directives.
	- $CPP_RESTRICTED
	- other environment variables

tidy up:
	- get rid of inlinedefs.h
	- use of places in and below macro.c is pretty bogus.
	- macro code should be reworked.

fix:
	- "#if 0 && 1/0" should not crash; fix eval method.
	- an unterminated comment is reported as "no newline at end of file"
	  (which isn't fatal by default)
	- the behavior of t26 is different here and in gcc -E -traditional