minor makefile tweaks

[Graham Percival]

1)  "make distclean" does not remove symlinks in ./out/    , such as 
./out/bin/* and ./out/share/locale/.  As a result, trying to grep for 
anything in the source tree produces a whole bunch of "No such file or 
directory" messages.  It's quite a minor thing, but still a bit 
annoying.

2)  Could "make -C python" be added to the "make web" rules?  I'm 
thinking specifically about make LILYPOND_EXTERNAL_BINARY here... it 
would be nice to advertise this possibility, and the "make -C python" 
line seems unnecessary for the user to type manually.

- Graham