asset guide, match application.rb snippets to the generated file [ci skip]

`if defined?(Bundler)` is no longer used in our current application.rb
cleanup, switch arguments in assert_equal calls
cleanup, assert on warning from postgres adapter
Fix that #pluck wasn't rescuing ThrowResult, meaning it would blow up when failing to construct_limited_ids_condition.
Add coverage for the fact that pluck without an argument returns all the table's columns.
No point in memoizing a simple literal string.
Make NullRelation a bit more like a real relation by returning 0 for #calculate(:count)
Rather than raising ThrowResult when construct_limited_ids_conditions comes up empty, set the relation to NullRelation and rely on its results.

This will help avoid errors like 2fcafee250ee2, because in most cases NullRelation will do the right thing. Minor bonus is avoiding the use of exceptions for flow control.
Fixes bug 10628.
Fix AM testcase break with mail 2.5.4. It seems that AM's testcase was wrong.
"normalize_callback_params" doesn't require name param
Eliminate minitest warnings

https://github.com/seattlerb/minitest/commit/9a57c520ceac76abfe6105866f8548a94eb357b6#L15R8
Merge pull request #10659 from vipulnsward/normalize_param2

"normalize_callback_params" doesn't require name param
Missing ending ``` at 14.2 Merging of scopes

http://edgeguides.rubyonrails.org/active_record_querying.html#merging-of-scopes
Merge pull request #10688 from elgalu/master

Missing ending ``` at 14.2 Merging of scopes
Fix typo in test name and documentation
Fix wrong `case_sensitive` in uniqueness validity test
Merge pull request #10691 from vipulnsward/typo_fix_ar_1

Fix typo in test name and documentation
Merge pull request #10692 from vipulnsward/fix_test_3

Fix wrong `case_sensitive` in uniqueness validity test
Merge pull request #10646 from kennyj/fix_am_20130517

Fix ActionMailer testcase break with mail 2.5.4.