fix(IHM): Fix regression introduced by commit #4874 (refs #4909)

The template's variable [isjs] was not correctly set
(uppercase/lowercase mismatch).

Also, when querying a data-foo="true" (or data-foo="false") property
with jQuery's data() function, the returned value is already a proper
true/false boolean (and not a "true"/"false" string).
Merge pull request #1233 from eguaj/3.2-A4909

fix(IHM): Fix regression introduced by commit #4874 (closes #4909)