experiments: support RunExperiment

Before the experiment code was just setting the need_to_store_experiment_data
option but nothing was looking at that option.  Rewrote the code, basing it on
InstawebContext::SetFuriousStateAndCookie, in order to actually set the cookie
to support the experiment.  There are tests for this functionality, but we're
waiting on issue #40 to be able to run them.

Manual testing (with line wrapping):

    $ curl -s -D- http://localhost:8050/mod_pagespeed_example/ | grep GFURIOUS
    Set-Cookie: _GFURIOUS=1; Expires=Fri, 01 Feb 2013 21:38:31 GMT;
                Domain=.localhost; Path=/

    $ curl -s -D- http://localhost:8050/mod_pagespeed_example/ | grep GFURIOUS
    Set-Cookie: _GFURIOUS=2; Expires=Fri, 01 Feb 2013 21:42:56 GMT;
                Domain=.localhost; Path=/

And it responds properly on receiving the cookie, although it did that before
this change too.
locking: support shared memory locking

Squashed merge of Otto's pull request #151.
Revert "locking: support shared memory locking"

I just enabled this on jefftk.com and it locked the server up.

This reverts commit d0464e8982f804da28b6762a3af681074663a857.
Add Debian's Install dependencies command
Merge pull request #157 from benoit934/patch-2

Add Debian's Install dependencies command
Revert "Revert "locking: support shared memory locking""

This reverts commit be9a78b18a8d415377cbcd547b24a62d99f94955.
shared-memory-locks: Fix a segmentation fault

Do not instantiate a ProxyFetchFactory when the ServerContext is
NULL on cfg_s
Merge pull request #158 from pagespeed/oschaaf-shared-mem-locks-fixed

Shared mem locks fixed
Merge branch 'master' into oschaaf-message-handler

Conflicts:
	src/ngx_pagespeed.cc
	src/ngx_rewrite_driver_factory.cc
	src/ngx_rewrite_driver_factory.h
	src/ngx_server_context.cc