Bug#929772: ResidualVM should be built against SDL2 instead of SDL 1.2

[Bastien Bouclet]

Package: residualvm

Version: 0.3.1+dfsg-1

I'm an upstream maintainer of ResidualVM and just noticed the version
packaged in Debian was build against SDL 1.2. At this point we recommend
linking against SDL 2, as ResidualVM can take advantage of the new
capabilities of that version. Our support of SDL 1.2 should be considered
as deprecated.

Please switch the dependency to SDL 2, the configure script should detect
it automatically.