Note possible further renaming of error properties (REnamer, 962112a)

At the moment I don't have a substitution error string and location but I may wish to add it in the future. In that case I'll need to rename the current "errorString" and "errorLocation" to "patternErrorString" and "patternErrorLocation" so as to differentiate them.

Signed-off-by: Greg Hurrell <greg@hurrell.net>