Fixed `columns_for_distinct` of postgresql adapter
Added documentation for the :param option for resourceful routing
Swallow bundler exceptions when running tests

Let's avoid useless output when testing stuff related to Bundler.
Remove unnecessary include for integration tests.
:scissors:
[ci skip] Fix Compiler's Github link
Speed-up TimeWithZone to String conversion

I've noticed that `String(model.created_at)` is performing poorly in comparision
with other fields. The source of the problem is a way `Kernel#String` works: it first
tries to call `to_str` (which causes `NoMethodError` in `method_missing`) and then calls `to_s`.

Performance tests:

    tz = Time.zone.now

    Benchmark.ips do |x|
      x.report { String(tz) }
    end

Without this code:

    Calculating -------------------------------------
                               572 i/100ms
    -------------------------------------------------
                            10177.7 (±18.2%) i/s -      48620 in   5.000325s

With this code:

    Calculating -------------------------------------
                              1518 i/100ms
    -------------------------------------------------
                           138984.2 (±10.1%) i/s -     677028 in   4.974897s
Clear inflections after test.
add a test for existing mapper functionality

I'm not sure if this is actually used, but I'm adding a test to define
the behavior
set defaults at the top so we can avoid the ||= test
extract controller checks to methods
reduce blank? checks
reduce action.blank? calls
fewer blank? calls
invert logic to remove nil? and exclude? checks (use ruby rather than AS when possible
trade 2 is_a? checks for a nil check
return early if we have a valid controller name
Merge pull request #15384 from zuhao/refactor_actionpack_params_wrapper_test

Clear inflections after test.
swtich to returning early if to responds to call
we don't need the call to presence. that is my present, to you!