silence a clang warning -Wcovered-switch-default

There's no reason to catch DEFAULT there anyways, most likely if
someone adds a new format to the enum, we want them to specify a
new extension for it.
silence a clang warning, "no newline at end of file"

This is apparently required by the C++ standard.
Silence many clang warnings [-Wmissing-variable-declarations]

warning: no previous extern declaration for non-static variable ...
Merge branch 'master' of git://github.com/wesnoth/wesnoth