bug #1007414 & patch #971730 - passivetex outputs "* 0.60 + 1em"

bug #1007414 & patch #971730 - passivetex outputs "* 0.60 + 1em"
garbage in lists (reported by Alex Roitman and James William Pye)

::PROBLEM
  Literal stuff "* 0.60 + 1em" showing up in listitem PDF output
  generated through passivetex

::CAUSE
  Logic that outputs non-constant size expressions like "4em *
  0.60 + 1em" was added to stylesheets to improve look of list
  formatting. But passivetex can only handle constant sizes; so,
  instead of doing the math, it spits out the literal expressions
  in output.

::FIX
  Added workaround - some conditional logic to fall back to
  constant values if passivetex.extensions param is non-zero.

::AFFECTED AREAS
  Should only affect FO output when passivetex.extensions is non-zero