Fix bug with merge form action when querystring is present.

[garrettc]

Querystrings are preventing the tags from merging, because get_full_path() in the redirect preserves querystrings.

Steps to reproduce

1. Load the admin area > Taggit > Tags
2. Sort by slug so that the path is /admin/taggit/tag/?o=2.1 (with querystring)
3. Select two tags, eg: "Adventure" and "Anthology, then action "Merge selected tags"

Result

Because the resulting path is /admin/taggit/tag/?o=2.1merge-tags/ you stay on the listing page.

This also affects paging querystrings.

Fix

Use request.path instead of request.get_full_path().

[rtpg]

Thanks for diagnosing this! Just changed this up a bit to call reverse directly instead of manually building up the URL, @garrettc would you be able to sanity check the changes I pushed up?

[garrettc]

@rtpg Looks good to me.

[rtpg]

alrighty, merging this! Thanks again