Modified _add_headers_to_tdata to accept list of Header objects

Ignore-this: 1df7ee56f5943c39bcfb24d67f867cda

darcs-hash:20090616094918-1e3d8-53d766b82504222a156f0861ea20b0d86607f397
Adapted sipsimple/core.util.pxi to new basic SIP objects

Ignore-this: b03f39950556f26878105828ac774723

darcs-hash:20090616095004-1e3d8-8969f7834b1e208a87c6a7d0302a6ef32b1786e3