Local variable cleanup

Some local variables were declared but not used. The variable xopt was
commented rather than deleted, since other commented lines seem to
depend on it.
delete old backup files, and all their pattern to gitignore
Local variable conflict

Local variable ‘tract’ renamed to avoid conflict with class ‘tract’
Small changes to variables

Fixed minor conflicts and definition problems
correct style to conform to PEP-8 in the examples

Mostly done automatically by the autopep8 tool.
Merge branch 'master' of github.com:DomNelson/tracts

A proper merge is not really possible, since the automatic styling of
the files with autopep8 on my end essentially rewrote the files, so git
is unable to figure out where the changes really are anymore (in
considers large swaths of program text to be different between the
branches.) To resolve this, I used the 'ours' merge strategy, and in
this merge commit, applied Dominic's changes by hand in the correct
locations.