Use strftime to convert DateTime to numeric

The native implementation of the seconds since the UNIX epoch in
strftime is significantly faster than our method.

Benchmark:
----------
require 'benchmark/ips'
require 'date'
require 'time'

date = DateTime.civil(1253,7,6,20,4,0)

Benchmark.ips do |x|
  x.report("strftime.to_i") { date.strftime('%s').to_i }
  x.report("ssue.to_i") { ((date - DateTime.civil(1970)) * 86400).to_i }

  x.report("strftime.to_f") { date.strftime('%s').to_f }
  x.report("ssue.to_f") { ((date - DateTime.civil(1970)) * 86400).to_f }
end

Output:
-------
Calculating -------------------------------------
       strftime.to_i     26480 i/100ms
           ssue.to_i     13818 i/100ms
       strftime.to_f     26561 i/100ms
           ssue.to_f     14479 i/100ms
-------------------------------------------------
       strftime.to_i   616937.3 (±2.4%) i/s - 3098160 in 5.024749s
           ssue.to_i   200108.8 (±6.9%) i/s -  994896 in 4.999278s
       strftime.to_f   553581.3 (±2.2%) i/s - 2788905 in 5.040397s
           ssue.to_f   204260.3 (±4.3%) i/s - 1028009 in 5.043072s
Remove DateTime#to_time override

Currently if the offset is not zero then to_time returns self which
can lead to errors where a developer assumes that the value is a
Time. To solve this we can use the native implementation of
DateTime#to_time in Ruby 1.9.3 as it handles offsets properly and
is faster than our override.
Remove rescue clause from ActiveSupport::TimeZone#to_f

Time#at no longer raises an error for large values so we can remove
the rescue clause from ActiveSupport::TimeZone#to_f.
Make Time#change work with offsets other than UTC or local

Use Time.new to create times where the current offset is not zero or
not in the local time zone - closes #4847 and #6651.
Merge pull request #6910 from mulder/fix_path_glob

Persist glob when replacing a path
Refactor migration test_helper

and create_join_table_test
Merge pull request #6914 from lexmag/migration_tests

Refactor migration test_helper
Unify the collation API for the database adpters
Revert "Use strftime to convert DateTime to numeric"

There appears to be a bug with DateTime#strftime("%s") on 32-bit platforms.
Bug report: http://bugs.ruby-lang.org/issues/6683

This reverts commit 210cd756a628cc19c0d6e44bee8c33dfb2d9d598.
Use strings for the table names

connection.tables returns an array of strings
Fix failing test related to persist glob when replacing a path

Introduced in pull request #6910, merged in 2ee3fa1a48513a2c42833e2e1f60fe03769bc295
remove :nodoc: of AR::Scoping#unscoped [ci skip]
Improve performance of DateTime#seconds_since_unix_epoch

Calculate the seconds since the UNIX epoch using the difference in
Julian day numbers from the epoch date. By reducing the Rational math
to just the offset component this gives a significant improvement.

Benchmark:

Calculating --------------------------------------------
       new     27733 i/100ms
   current     15031 i/100ms
       new     27737 i/100ms
   current     15549 i/100ms
--------------------------------------------------------
       new   548182.1 (±0.9%) i/s - 2745567 in 5.008943s
   current   216380.9 (±1.6%) i/s - 1082232 in 5.002781s
       new   510281.9 (±1.2%) i/s - 2551804 in 5.001525s
   current   219858.3 (±1.8%) i/s - 1103979 in 5.023039s
Made file name and class name consistant
Merge pull request #6919 from rahul100885/master

Make file name and class name consistant

Related to dbc43bcce69aa4aaf0ae309bf410e2b786c4e3f6
push response creation down since third param is never used.
explains why the file update checker ignores mtimes in the future, plus a little refactor for the same price
Update 4.0 Release Notes with changelogs [ci skip]

Also fix some wrong formatting.

Related discussion:
https://github.com/rails/rails/commit/ab72040b74f742b6676b2d2a5dd029bfdca25a7a#commitcomment-1525256
Don't mark the store as changed if an attribute isn't changed.
Merge pull request #6934 from kennyj/fix_store

Don't mark the store as changed if an attribute isn't changed.