Lock elision tuning interface

[Andi Kleen]

This patchkit is an updated version of the glibc elision tuning
interface through environment variables. An earlier variant
of this code was in the original elision code submission,
but was not added.

This version updates it to include a white list through
a configuration file. This allows to disable it as needed,
when there are concerns that changing elision parameters
may impact root programs.

The white list can also be enabled/disabled at build time. 

I would like to have the environment interface because
it gives more flexibility to distributions. For example
they can disable elision by default, but still allow 
users to override that choice. Or enable it by default,
but allow disabling if needed. In addition it also
allows to tune the various retry parameters.

I also included the test code and the manual
that did not make it in last time.

-Andi