Remove useless constant.
glade/liferea.ui: remove "copyright" from the About dialog

It was of low value and the listing of the years was a constant
nuisance for translations.
Removing dead duplicated code (suggested by Adrian Bunk)
src/migrate.c must #include "export.h"

for getting the prototype of import_OPML_feedlist()
src/feedlist.c must #include "comments.h"

for getting the prototype of comments_deinit()
src/export.c: add missing #include's of auth.h and db.h
src/browser_history.h: add a prototype for browser_history_add_location()
typo fixes: wether -> whether
src/vfolder_loader.c must #include "ui/ui_node.h"

for getting the prototype of ui_node_update()
Fix a typo in an assert in src/main.c:on_feed_add()
Remove an unused variable in src/main.c:on_app_activate()
Remove an unused variable in src/ui/feed_list_view.c:feed_list_view_select()
Remove the stale src/ui/ui_common.h:ui_choose_directory() prototype
src/ui/ui_common.h: Remove GTK+ < 3.0 compat code
Limit #include "ui/ui_common.h" to the files actually using it
src/ui/enclosure_list_view.c doesn't need #include "ui/preferences_dialog.h"
Remove an unused variable in src/subscription.c:subscription_import()
Remove unused variables from src/itemlist.c:itemlist_remove_all_items()
Updated the default feedlists

The Russian feedlist was in a state where deletion was the best option.
.gitignore: add ar-lib (from automake)