Make QScriptEngine::importExtension() more efficient

The importExtension() function is a little inefficient.
It loads every script plugin and queries each one for the imported extension
name. Would it be possible to modify this to first try the "obvious" plugin
based on the name of the extension, and only fall back to a full scan if it
isn't found? Loading every script plugin on a Qtopia handset would be
expensive if the program only needs to use PIM or Telephony settings.