I am somewhat reluctantly changing the API so that setProcFD is no longer

I am somewhat reluctantly changing the API so that setProcFD is no longer
idempotent with regards to global state. But Julien Tinnes convinced me that
we should try to hold on to /proc for as short a time as possible.

This change potentially makes things a little more difficult for callers, as
they can now no longer re-use the file descriptor passed into setProcFd(), so
I updated the comments to warn about the changed semantics.

BUG=n/a
TEST=make test
Committed: https://code.google.com/p/seccompsandbox/source/detail?r=186

[Markus (顧孟勤), 2012-05-21 22:54:19]

I am not incredibly happy about this change, as it conceivably makes things a
little more difficult for the users of this code. But Julien convinced me that
we need this.

[jln (very slow on Chromium), 2012-05-21 23:05:41]

On 2012/05/21 22:54:19, Markus (顧孟勤) wrote:
> I am not incredibly happy about this change, as it conceivably makes things a
> little more difficult for the users of this code. But Julien convinced me that
> we need this.

LGTM