use boost mersenne twister rng, add boost::random dependency

This is a squash of work done in april, see closed github pull
request. #160
add ~SCALE_SHARP image path function, analogous to ~SCALE

The syntax is the same but it uses nearest neighbor instead of
bilinear interpolation
update changelog
add ~Alpha image path function

Mainly useful as a diagnostic tool
add ~Wipe_Alpha image path (mainly a diagnostic tool)
rename IPF functions
Merge pull request #322 from cbeck88/boost_rng_squash

use boost mersenne twister rng, add boost::random dependency
move SDL_SavePNG to the wesnoth_sdl lib target

This is to possibly fix issue shadowm reported, and keep all the
things that SDL depends on together.
mention boost random in release notes
update RELEASE_NOTES to contain the resolution of the BFS saga
update changelog
Display the campaign's icon in the create multiplayer dialog.
Update Xcode project file with new libboost_random dependency

This also requires a new version of the Mac compile package.
output compiler version info in the travis logs
Merge branch 'master' of https://github.com/wesnoth/wesnoth
move cxx version check to after we install compiler upgrade
fixup C++11 compilation, thanks to duncan_shriek/roland_ on irc
add a CXX11 build to travis
fixup travis
fixup .travis.yml