preheat habtm column cache
fix the variable name
`intiantiated` => `instantiated` [ci-skip]
Merge pull request #12430 from vipulnsward/changelog_fix

`intiantiated` => `instantiated` [ci skip]
Fix a typo in the code of Testing guide.

Replace the word «Accepts» by «Accept» in the example of custom request headers.
Merge pull request #12431 from GRoguelon/master

Fix a typo in the code of Testing guide. [ci skip]
Merge pull request #8791 from griffinmyers/master

Updated DirtyModel's @changed_attributes hash to be symbol/string agnostic

Conflicts:
	activemodel/CHANGELOG.md
map the association chain to table names
Port test from cf1904f to avoid future regression

Related issue: #11939, #12084
Merge pull request #12435 from sikachu/master-port-12084

Port test from cf1904f to avoid future regression
Fixed typo in documentation
require the files we need so the classes are stand-alone
parent is always passed in, so make it non-optional
simplify the JoinAssociation constructor, check validity *before*
Set the join type on construction

We always set the join type immediately after construction, just make it
part of the constructor and we can skip that step
Always pass parameters to `build`

We always know the parameters in advance, so we don't need to build it
in to the method signature
hashes are ordered, so we do not need to sort
Fixed return strings in documentation
inject down the hash cache
Directory name in RUNNING_UNIT_TESTS.rdoc [ci skip]