Use only the page relevant pieces in the parser cache key. Eg. two users with different math options will now
use the same parsercache entry for articles without <math> tags.
The cache key format is kept as a fallback so the old cached entries can be reused.
Should boost parsercache hits, but it also makes easier to pollute the parsercache by tag hooks that behave
badly, directly using $wgUser or $wgLang.
Extensions hooking PageRenderingHash now see !edit=0 and the !printable=1 bits.
Fixes bug 24714 - Usage of {{#dateformat: }} in wikis without $wgUseDynamicDates can lead to unexpected results
Builds upon r70498, r70498, r70501, r70517, r70651, r70653, r70765, r70780.