ACTION-123: Measurements Note AI: Fold PE warm-up and cache subsubsection with Measurement Integrity subsection

Measurements Note AI ai-doc (contribute text):
GW: Fold PE warm-up and cache subsubsection with
Measurement Integrity subsection

http://www.w3.org/XML/Group/EXI/docs/meas/exi-meas.html

Try to remember what it was, assign date based on that.

Asked JS to write cache subsection of Measurements Integrity and Reproducibility Criteria based on his emails for ACTION 96. If he can\'t, replace text deleted from Jaakko\'s last para of Warm-up and Caching of Measuring Processing Efficiency, but add more regarding distinction of network and loopback, and distinguish between what he calls \"unrealistic\" and \"realistic\" cache effects.