Fix an issue with population of FK fields using autocomplete.

The fix comes from a comment by Dmytry Scherbina in a pull request
originally submitted by Jakob Klein.
Fix multiple bugs related to GPC parameters pollution from code

Was introduced by me in e1a5b9c54f3ea112a0ce5b2f0f3a0ace9583a354 while
trying to make parameter more plugin friendly. display.php code default
code use a defined set of GPC parameter and make them persitent between
two call (while paging or sorting data). Any other parameter is ignored
and doesn't survive a new call. This patch attempted to make plugin
specific GPC parameters persistants, but was making ALL parameters
persitants, introducing a bunch of bug.

This one revert part of this previous patch but keep the small
house-cleaning.