Add previously missing -Wall to warning flags in CMake. Remove -Wformat
and -Wvariadic-macros (enabled by default; latter is not meaningful in
C99 mode we use), -Wdeclaration-after-statement (again, not needed as
we use C99). Move -Wmissing-declarations to C-only flags (GCC man says
so).
Add copyrights year to crypto-utils-fallback.c.
1. add the option the code to be used under GPLv2 or GPLv3; previously only GPLv2 was allowed
2. add the "proxy option" as described in GPLv3 so we can add future licenses without having to bulk-edit everything again :)
3. remove the awkward "exception for MIT code in Mac client" clause; it was unnecessary and confusing.
