Bug and fix in -me macros

[Ted Hopp]

Description:

	This happened with version 2.9 of -me (version 2.1 of sh.me).

	I defined the macro '$0', which is automatically called
	from 'sh' when starting a new section, to log the section
	name in a Table of Contents index.  Occasionally '$0' would
	get a null string as the section name.  This occured when
	'$p', which prints the section header for 'sh', triggered
	a trap that causes an index entry to be generated.  (I am
	floating figures and entering the figure captions in a List
	of Figures index when the figure is output.)  Because of
	the delayed processing of the index entry macros when they
	are in a diversion such as a floating keep, they execute
	during the trap processing.
	
	The string '|x' is used by 'sh' to temporarily store the
	section header, but it is also used by ')x' to store the
	page number for the index entry.  This destroys the value
	of '|x' for 'sh', so '$0' gets a null string.

Repeat by:

	Playing around with the location of a trap that causes
	the index entry macros to be called just when a section
	header is to be printed.  Define '$0' to do something
	with the section name; it will get a null string.

Fix:

	I fixed 'sh' in \*(||/src/sh.me to redefine |x just before
	calling '$0'.  This seems kind of a kludge, but it works.

	Old:

		.if !"\\$2"_" \
		\{\
		.	ds |x \&\\$2
		.	$p "\\*(|x" "\\*($n" \\n($0
		.	$0 "\\*(|x" "\\*($n" \\n($0
		.	rm |x
		.\}

	New:

		.if !"\\$2"_" \
		\{\
		.	ds |x \&\\$2
		.	$p "\\*(|x" "\\*($n" \\n($0
new -->		.	ds |x \&\\$2	\" in case |x got clobbered
		.	$0 "\\*(|x" "\\*($n" \\n($0
		.	rm |x
		.\}

	Is there a more elegant solution?  I thought of calling
	'$0' from '$p', but '$p' is called from 'sx' with no call
	to '$0'.  The real fix is to avoid conficting uses of '|x',
	but I'm too lazy to figure out how to do that.
-- 

Ted Hopp	{seismo,umcp-cs}!nbs-amrf!hopp