Finds the program that is associated with an extension.
The extension may or may not begin with a '.'. Note that
a <code>Display</code> must already exist to guarantee that
this method returns an appropriate result.
@param extension the program extension
@return the program or <code>null</code>
Finds the program that is associated with an extension. The extension may or may not begin with a '.'. Note that a <code>Display</code> must already exist to guarantee that this method returns an appropriate result.
@param extension the program extension @return the program or <code>null</code>