Hi,

I would like to submit a tiny patch to make use of `org-clock-string'
instead of the hard coded value CLOCK: whenever possible.

I also found out that :CLOCK: was hard coded in
`org-insert-property-drawer' (git sha
67ae102b4be87976240555d1c0d80ee55906f53c, file lisp/org.el:15897)
instead of using `org-clock-drawer-start-re' but I did not have time to
fix this one.

Please find the patch attached to this mail.