make_ctags change

Exuberant ctags adds data at the beginning of the tags file. It also sorts
the tags file by default. This means, if we sort the file generated by
Exuberant ctags, it doesn't work in VIM and possibly other editors.

I didn't notice this until recently because I was using my own script. Its
possible that this only affects recent version of Exuberant ctags though I
tested a version from 2001 which exhibited the same behaviour.

Gavin