adds guides/.document to tell rdoc not to process this directory

When the Rails 4 gem is installed rdoc sees markdown files below the
guides directory and processes them. With an empty .document file
we prevent that from happening. Thanks to @drbrain for the tip.
Fix WhereChain docs to mention only not
Call String#gsub with Hash directly
Merge pull request #9554 from tmm1/string-gsub-hash

Use 1.9 String#gsub syntax
Use ActionView::OutputBuffer#safe_append= from templates
avoid extra method calls for appending newlines

before:

        ');@output_buffer.append= ( content_icon row[:content] );@output_buffer.safe_concat('
');@output_buffer.safe_concat('        ');@output_buffer.append= ( spinner_img );@output_buffer.safe_concat('
');@output_buffer.safe_concat('      </td>
      <td class="content">
        ');@output_buffer.append= ( content_link row[:content] );@output_buffer.safe_concat('
');@output_buffer.safe_concat('      </td>
      <td class="message">
');

after:

        ';@output_buffer.append=( content_icon row[:content] );@output_buffer.safe_append='
        ';@output_buffer.append=( spinner_img );@output_buffer.safe_append='
      </td>
      <td class="content">
        ';@output_buffer.append=( content_link row[:content] );@output_buffer.safe_append='
      </td>
      <td class="message">
';
Remove reference to BugMash. Link hasn't been updated in 4 years.
change useless gsub to delete
strong parameters example for default values using `fetch`. [ci skip]

Origin: #9534.
example for `accepts_nested_attribtues_for` and strong parameters.

Closes #9558.
Merge pull request #9556 from senny/strong_params_examples

strong parameters example for default values using `fetch`.
Fix typo in AC overview guide [ci skip]
Merge pull request #9557 from bonsaiben/useless_gsub

Change useless gsub to delete
Fix typo
Routing match `via` option requirement exception message made more explicit
Merge pull request #9561 from inossidabile/explicit_match_via_requirement_exception_message

Routing match `via` option requirement exception message made more explicit
assigning '0.0' to a nullable numeric column does not make it dirty
Merge pull request #9042 from senny/9034_float_0_0_is_always_dirty

Assigning '0.0' to a nullable numeric column does not make it dirty

Example:
    product = Product.create price: 0.0
    product.price = '0.0'
    product.changed? # => false (this used to return true)
    product.changes # => {} (this used to return { price: [0.0, 0.0] })
transactional migration test-case was broken.

The cleanup commit a85625d broke the test-case.
The schema was no longer modified so there was no
way to check that the rollback actually happened.
change useless gsub to tr