Miscellaneous scripts, utilities, etc. Fresh nectar is welcome

$ ./travis/cpp/gcc_update.sh --version 4.9

This script updates travis default GCC version. Parameters:

• -v/--version: GCC version, dot syntax.
• -r/--repository: Ubuntu repository to get GCC update from.

$ ./travis/cpp/clang_update.sh --version 3.4

This script updates travis default Clang version. Parameters:

• -v/--version: Clang version, dot syntax.
• -r/--repository: Ubuntu repository to get Clang update from.
• --libc++: Build libc++ library. Note this does not add -stdlib=libc++ -lc++abi and related flags to your compiler. Don't forget to pass libc++ headers (/usr/include/c++/v1/) to your compiler include path to fully override default stdlibc++.
• --libcpp-upstream: URL of the SVN repository with libc++ sources.