Suggested by G. Brandon Robinson.

The overloading of IR emits magic \X'...' sequences that turn into HTML manual links. But not all such IR invocations should be manual links; those had to be written to avoid the IR macro before. Worse, the \X'...' ending the IR causes troff to emit only a single space after a period. Defining a new IM macro for manual references fixes both problems. Fixes #441.

Fixes #386.

dd fans rejoice! Also helps with commands like go test -run=x.

This fixes at least one shell script (printfont) that expected 'x'`{y}'z' to mean 'x'^`{y}^'z' as it now does. Before it meant: 'x'^`{y} 'z' One surprise is that adjacent lists get a free carat: (x y z)(1 2 3) is (x1 y2 z3) This doesn't affect any rc script in Plan 9 or plan9port.

http://codereview.appspot.com/105061