phobos dependencies

[Andrei Alexandrescu]

http://chopapp.com/#fvepfd8 shows the number of dependencies (plus 1) 
for each module in phobos. Those include druntime dependencies.

With https://github.com/D-Programming-Language/phobos/pull/1768 
dependencies would be generated automatically, which should be a good 
step toward reining in.

The zsh command I ran was  wc -w generated/**/*.deps | sort -nr.


Andrei