add patch for poco headers

this patch should transparently apply the changes @arturoc et al made to the poco headers, whilst retaining upstream compatibility with poco.

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
update poco recipe to apply header file patch

* applies patch to header files in copy stage

* add commit hash for poco source so that only approved version of poco source will be checked out.

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>