Changes for Inform 7 (build 6L02)-It builds! Yeah!

Various changes to allow for the story to be built in the new Inform 7
(build 6L02).
The two phrase definitions 'To decide which number is the absolute value of (N - a number)' [line 33 of story.ni]  and 'To decide which real number is the absolute value of (R - a real number) (documented at ph_absolutevalue) (this is the abs function)' [line 5127 of /Applications/Inform.app/Contents/Resources/Inform7/Extensions/Graham Nelson/Standard Rules.i7x] make the same wording produce two different kinds of value, which is not allowed.