org-bibtex: Fix docstrings

* lisp/org-bibtex.el (org-bibtex-inherit-tags,
org-bibtex-no-export-tags, org-bibtex-tags-are-keywords): Fix
docstrings.

lisp/org-bibtex.el

@@ -263,32 +263,34 @@ IDs must be unique."
 
 (defcustom org-bibtex-tags-are-keywords nil
   "Convert the value of the keywords field to tags and vice versa.
-If set to t, comma-separated entries in a bibtex entry's keywords
-field will be converted to org tags.  Note: spaces will be escaped
-with underscores, and characters that are not permitted in org
+
+When non-nil, comma-separated entries in a bibtex entry's keywords
+field will be converted to Org tags.  Note: spaces will be escaped
+with underscores, and characters that are not permitted in Org
 tags will be removed.
 
-If t, local tags in an org entry will be exported as a
-comma-separated string of keywords when exported to bibtex.
-If `org-bibtex-inherit-tags' is t, inherited tags will also
-be exported as keywords.  Tags defined in `org-bibtex-tags'
-or `org-bibtex-no-export-tags' will not be exported."
+When non-nil, local tags in an Org entry will be exported as
+a comma-separated string of keywords when exported to bibtex.
+If `org-bibtex-inherit-tags' is non-nil, inherited tags will also
+be exported as keywords.  Tags defined in `org-bibtex-tags' or
+`org-bibtex-no-export-tags' will not be exported."
   :group 'org-bibtex
   :version "24.1"
   :type 'boolean)
 
 (defcustom org-bibtex-no-export-tags nil
   "List of tag(s) that should not be converted to keywords.
-This variable is relevant only if `org-bibtex-tags-are-keywords' is t."
+This variable is relevant only if `org-bibtex-tags-are-keywords'
+is non-nil."
   :group 'org-bibtex
   :version "24.1"
   :type '(repeat :tag "Tag" (string)))
 
 (defcustom org-bibtex-inherit-tags nil
   "Controls whether inherited tags are converted to bibtex keywords.
-It is relevant only if `org-bibtex-tags-are-keywords' is t.  Tag 
-inheritence itself is controlled by `org-use-tag-inheritence' and
-`org-exclude-tags-from-inheritence'."
+It is relevant only if `org-bibtex-tags-are-keywords' is non-nil.
+Tag inheritence itself is controlled by `org-use-tag-inheritence'
+and `org-exclude-tags-from-inheritence'."
   :group 'org-bibtex
   :version "25.1"
   :package-version '(Org . "8.3")