Stop setting WITH_UIP6=1 in example Makefiles

It achieves exactly nothing other than generate confusion
Don't specify -DUIP_CONF_IPV6 in platform makefiles

Makefile.include has done it for us already, we no longer need to do so ourselves
A massive all-tree automated update of all double inclusion guard #defines that changes from using two underscores as a prefix, which are reserved, to not using two underscores as a prefix
Fix: preserving blank characters (tabulator and space) in Cooja serial output
Merge pull request #462 from adamdunkels/push/no-reserved-double-inclusion-defines

Remove all leading double underscore inclusion #defines
Merge pull request #428 from g-oikonomou/config-sanity

Remove unnecessary stuff from various Makefiles (Config Sanity, Pt 1)
Merge pull request #469 from eberlin/cooja-tab-char

Fix: preserving blank characters (tabulator and space) in Cooja serial output