Recommit: local.c: avoid a NULL dereference on error.

A re-commit of https://github.com/berkley4/polipo/commit/150f4c79e9f7143a57ec876a8cd98f3c2c172269 minus the return statements
which were a major part of upstream commit https://github.com/jech/polipo/commit/6bb7900e512f2391a957801723d326c3ed3450a7
Recommit: Log request allocation failures

Part of the patch listed here :-
https://trac.torproject.org/projects/tor/ticket/2207

Nearly trailing whitespace was also deleted.

Re-committed because of the reversion https://github.com/berkley4/polipo/commit/98dddeb1c68e2625933bb4afa6dc3860c6af8c0b
Recommit: server.c: Fixing unused variable.

  * I'm not sure of the second part... [this bit stays reverted]
  * but calling httpServerAbort looks logical to me.

Re-committed minus the second part because of the reversion https://github.com/berkley4/polipo/commit/e42422052be41bf3df2df28867cc498a5f8a36e4