Bug #6255. Wrap gzip files with TextIOWrapper to allow them to be read as text.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21177 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
Fix undefined variable reference, make separate not-loaded warning

Thanks to Pat Lefebre for reporting the error.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21179 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
Fix platform detection on OSX

'darwin' is returned by sys.platform, not os.name.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21180 4ae1f11a-8b86-4847-b8af-ab372f36d1fd