RFE: better support for patching setup.cfg files

[yazug]

commonly when openstack python packages are tagged upstream the setup.cfg file is re-written and whitespace normalization is done for the version of the setup.cfg that is in the tarball vs what is in the branch.

this causes most attempts to patch setup.cfg to fail when trying to build with that patch in the %prep section

It would be nice if rdopkg could at a minimum detect failure to apply patch to tarball downloaded.

for bonus points gracefully handling the simple tabs vs spaces and trailing space at end of line after an = cleanly.

[yac]

This is related to #110