This gives us a few benefits:
1) make -j clean all
   this will start working, as it should. It currently doesn't.
2) increased parallel build
   recursive make will max out at number of files in a directory,
   non-recursive make doesn't have such a limitation
3) Removal of duplicate information in make files,
   less error prone

I've also slightly updated how we call AM_INIT_AUTOMAKE, as the way
that was used was not only deprecated but will be *removed* in the next
major automake release (1.13).... so probably best that we can continue
to bulid tor without requiring old automake.
(see http://www.gnu.org/software/automake/manual/html_node/Public-Macros.html )

For more reasons  why, see resources such as:
http://miller.emu.id.au/pmiller/books/rmch/