make difference more clear between save and save! in doc

[pseidemann]

adapts changes proposed at https://groups.google.com/forum/#!topic/rubyonrails-core/Py9x8rLaxgQ.
related to #20662.

changes the documentation of save by adding "attempts" to the first paragraph and setting the paragraph about "validations can abort the action" as the second paragraph.

[repinel]

Wouldn't this leave the documentation for methods like update_attribute and update inconsistent?

In your point of view, they attempt to update, but something can happen and they'll return false.

[arthurnn]

Wouldn't this leave the documentation for methods like update_attribute and update inconsistent?

yes.

Maybe we should change this part instead:

-     # By default, save always run validations. If any of them fail the action
-     # is cancelled and +save+ returns +false+.
+     # By default, save always run validations. If any of them fail the action
+     # is cancelled and +save+ returns +false+ and the record wont be saved.