Remove the version_info copy constructor.

Its behaviour was identical to the compiler generated version.

git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56431 75b3775d-3801-0410-9e12-e2e43121521d
Fixing a comparison with the wrong member.

Discovered while looking at SDL 2.0 code.

git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56432 75b3775d-3801-0410-9e12-e2e43121521d
Add SDL 2.0 compatibility.

Remove the INPUT_MASK define. Its usage is replaced by the functions:
- is_input
- discard_input
This also removes most external users of the discard function, which is
also problematic due to the event mask.

git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56433 75b3775d-3801-0410-9e12-e2e43121521d