While there were some changes to how custom JavaScript is executed in Forms 10.2, I don't have any issues using $.getScript and using functions defined in custom files saved to a subfolder of /Forms/js.

Building off of what Xavier had mentioned:

1. If you type in the URL http://DEV_LF/Forms/js/AvisFleetCustom/Common.js into the navigation bar of the browser, do you indeed get the JavaScript file back?
2. Are there any errors in the browser console (F12 > Console) when loading the form?
3. You can use the followng code to further debug $.getScript :

   $.getScript(/* JS file URI */, function(data, textStatus, jqxhr) {
     console.log(data);
     console.log(textStatus);
     console.log(jqxhr.status);
   });

   This code will log to the browser console some information, in order:

   1. Any data returned from the request; if successful, this will be the contents of the requested JavaScript file.

   2. The status of the response; if successful, this will be the string 'success'.

   3. The HTTP status code of the response; if successful, this will be 200.

I tested with similar script with Forms 10.2 update 1 and popup is a function defined in testapi.js, there is no problem to execute it.

$(document).ready(function () {

    $.getScript("http://v-sh-lf102/forms/js/util.js",function(){
     $.getScript("http://v-sh-lf102/forms/js/util.redirect.js",function(){
    $.getScript("http://v-sh-lf102/forms/js/testapi.js");
    });
    });
  $('#q92 input').on('click',clear);
  function clear()
  {  
  popup();
}
});

Where is the blcokUI defined in your script?