Change 1.26 to 1.27, mostly in doc comments

Change 1.26 to 1.27, mostly in doc comments

Using the following command line, I have found doc comments (and
a wfDeprecated() call) mentioning "1.26" when they should mention
"1.27" instead, which I have fixed manually:

git diff -M REL1_26 | grep --color=always -C 10 -iP \
'^\+.*\D1\.26(\D|$)' | aha > oldver.html

Follows-up these commits:
* 047b60b96d8218eec5122dbca38e367773267d4b
* 169b7b98b5c43db55acfc7e31b089300c0026c80
* 25a44aa3e4fa511d326b373af71762eb7375db7a
* 2fb2a3f14b34d4b81de2ca1aec07efc5659f9e90
* 3f1e9fa268cdc9850dd1df2b271dbd814d957488 [1]
* 8c84af70b656678dea7845eee6acbfe7ced6d6f9
* c0cb80beac069254edf9f77b7ce149af6568be23
* d04a92a5517d656447d73001e51a8cfb9b130d07
* d3b85592ead7fc1348c20c565fd21375da5417de

[1] Release notes moved in I195dd1cf.

Because a release note stating that the UserRights hook is deprecated
was added in 37062a0c0d0b (before the branch cut), this commit does not
change the Hooks::run call that had been changed in 21206c8fbe90.

Change-Id: I5a427f003e7e3b4559fe377bcdfdca466a570708