### Summary
There was an issues when using `safe_constantize` on a string that has
the wrong case.
File `em.rb` defines `EM`.
`"Em".safe_constantize` causes a little confusion with the autoloader.
The autoloader finds file "em.rb",
expecting it to define `Em`, but `Em` is not defined.
The autoloader raises a `LoadError`, which is good,
But `safe_constantize` is defined to return `nil` when a class is not found.
### Before
```
"Em".safe_constantize
LoadError: Unable to autoload constant Em, \
expected rails/activesupport/test/autoloading_fixtures/em.rb to define it
```
### After
```
"Em".safe_constantize
# => nil
```
In the following situation:
```ruby
class Bar
end
module Baz
end
class Foo
prepend Baz
end
class Foo::Bar
end
```
Running `Inflector.constantize('Foo::Bar')` would blow up with a NameError.
What is happening is that `constatize` was written before the introduction
of prepend, and wrongly assume that `klass.ancestors.first == klass`.
So it uses `klass.ancestors.inject` without arguments, as a result
a prepended module is used in place of the actual class.
Xavier Noria