make doesn't find modified files

[Graham Percival]

"make blah blah web" no longer finds modified files.  I made a number 
of changes to instrument-notation.itely, but "make web" reports 
instrument-notation.texi as up to date and doesn't incorporate the 
changes in the output.  I deleted everything in out-www/ to force it to 
redo the entire manual, but this takes a lot time.  :(

Cheers,
- Graham