* lisp/ob-exp.el (org-babel-exp-process-buffer): Change variable
name `org-export-babel-evaluate' to `org-export-use-babel'. Also
change the name in its `defcustom' and set the `:safe' key.
* lisp/ox-icalendar.el (org-icalendar-export-current-agenda): Change
variable name.
* lisp/ox.el (org-export-as): Change variable name.
* doc/org.texi (Exporting code blocks): Change variable name. Amplify
the explanation of what the variable does. Add variable index entry.
* testing/lisp/test-ob-exp.el: Change variable name.
* testing/lisp/test-ob-lob.el: Change variable name.
* testing/lisp/test-ox.el: Change variable name.
Users were often confused that setting this variable to `nil' will
cause header arguments to be ignored in addition to preventing code
from being evaluated. It is hoped that the documentation changes and
the name `org-export-use-babel' will better convey that everything
babel does can be switched off with this variable.