Issue #17011: Fix caching of xpath path when namespaces are present.

Thanks to Stefan Behnel for the report and proposed solution & test.
Issue #17902: Clarify doc of ElementTree.iterparse
Issue #17684: Fix some test_socket failures due to limited FD passing support
on OS-X. Patch by Jeff Ramnani.
Silence compiler warning about an uninitialized variable
Silence compiler warning for an unused declaration
Issue #18151: Replace remaining Idle 'open...close' pairs with 'with open'.
Silence compiler warnings for strict function prototype declarations.
#18657: remove duplicate entries from Misc/ACKS.

Patch by Madison May.