Remove non-relocatable poly1305 implementation

This follows the recommendations to build a shared NaCl from
http://wiki.ucis.nl/NaCl/Shared.  The build will fall back on a portable
implementation.
Compile with -fPIC for relocatable objects

Following http://wiki.ucis.nl/NaCl/Shared.

* okcompilers/c: Add -fPIC to the compilers.
Build in build/, not build/$hostname.

* do: Build in build/, not build/$hostname.
Only build for the default target architecture.

Also, print output when building.

Includes patch from Bartosz Fenski <fenio@debian.org>:
http://patch-tracker.debian.org/patch/series/view/nacl/20110221-4.1/compiler_flags

Includes patch from Peter Michael Green <plugwash@debian.org>:
http://patch-tracker.debian.org/patch/series/view/nacl/20110221-4.1/output-while-building
Add Makefile, and shared library target

* shared.c: New file, downloaded from
  http://oss.ucis.nl/nacl/shared/shared.c, following
  http://wiki.ucis.nl/NaCl/Shared.  I did not apply the "randombytes"
  patches.

* Makefile: New thing.
update README