Make sure all files in MariaDB have proper license headers

While packaging MariaDB for Debian I noticed that there are many source files that lack proper license headers. For the sake of clarity and machine parseability if would be good if all source files would have proper license headers.

The output of "mariadb$ licensecheck --copyright -r . -c ." showing many files with license UNKNOWN is at http://labs.seravo.fi/~otto/mariadb-repo/mariadb-5.5.34-license-headers.txt

Just to make is explicit: I didn't find any legal issues while looking at the licenses. Many folders have folder wide copyright files etc instead of per file headers, so from a legal perspective things are ok, this is just a markup issue.