Rejig DEFINES and EXTRA_DEFINES

Explicitly declare EXTRA_DEFINES and transpose the DEFINES and CFLAGS
declarations so that all the DEFINES subcomponents are together.

EXTRA_DEFINES is blank by default, but anyone customising their
makefile can now make their choice more easily.
removing some warnings

+ Non-author changes to origial patch:

  * Surrounding trailing whitespace cleaned up.
Minor typo in log message
Add a couple of failure warnings

Taken from the patch listed here :-
https://trac.torproject.org/projects/tor/ticket/2173
Optionally avoid transmitting sensitive system information

This adds the dontIdentifyToClients option. When set to true, try to avoid
transmitting local host name, port, and time zone. When Polipo is
used with Tor, this information might be useful to an adversary
who wants to identify an anonymous user.

This issue was raised by Gregory Fleischer in his DC 17 presentation,
"Attacking Tor at the Application Layer".

http://pseudo-flaw.net/resource/defcon/attach:/defcon-17-fleischer.pdf
http://pseudo-flaw.net/content/defcon/dc-17-demos/

+++ Non-author changes +++

This change combines the following commits into a single commit :-

https://github.com/jech/polipo/commit/c78beb81e506683a2dc29cfa2eae3c438652585e
https://github.com/jech/polipo/commit/b77065f150546a29a92ac468dbaed88aaf53a9b4
https://github.com/jech/polipo/commit/be116b561321cddc1e1a474e6cefcbf58b7b5e44

Minor trailing whitespace cleanup.
Respond to change in resolv.conf when using the system resolver When using Polipo's own (asynchronous) DNS implementation, Polipo still only reads resolv.conf once, upon startup.

Taken from the patch at https://industry.youview.com/resources/opensource/patches/polipo-1.0.4.1/0011-DEVARCH-4284-HTTP-Cache-Polipo-responds-to-change-in.patch
Fix pid_t redefinition error

(cherry picked from commit 2280e584a0e41d40dfe1adf93d6967f9a020e6a4)
Log request allocation failures

Part of the patch listed here :-
https://trac.torproject.org/projects/tor/ticket/2207
Add DCHUNK_SIZE to Makefile along with a description