Correct YUnitLabels for All Reduction Results

[PeterParker]

From Richard, as a result of testing http://trac.mantidproject.org/mantid/ticket/9710:

Very minor issue:

http://trac.mantidproject.org/mantid/ticket/9710 Y axis units, “front” and “rear” detector data still get old units 1/cm when produced as part of a “merged”reduction, “rear” detector gets old units when part of a “both” reduction

Ie I think it is only putting the new units on the last one generated thus can still get some: You are overlaying plots from data having differing units!

[PeterParker]

This issue was originally trac ticket 9836