Fixed several bugs in product list screen

Fixed the following bugs in the product list screen:
 - The inUseOnly flag is now carried over to the next screen
   when a user reorders the list by a given field. Previously
   reordering the list revealed both in use and not in use
   items regardless of what original option was selected.
 - The PHP script now autofills in variables that are not
   set in the _GET request. Previously the script assumed
   certain variables (such as manufacturer) were always in
   _GET array, which is not the case
Merge branch 'master' of github.com:mariposacoop/IS4C