test a working copy with identical files

This test suite creates a working copy with files with identical contents.  The
two files are created on different commits.  It exposes a couple of problems:

- Git: thinks the two files were made on the same commit
- Hg: doesn't report the commit
clean up and make CopyTest more robust

Test now considers three files:
  * an original file
  * a file with the same contents as the first
  * a file which also had the same contents, but has changed
    somewhere in between, and reverted

Other functional changes:
  - add new file to other test cases
  - removed some unnecessary flags
  - remove test_log2 altogether since it doesn't seem to add much

Other non-functional changes:
  - add some comments to describe the working copy created
  - coding style matching
Merge branch 'feature/fix-copy-cache' of https://github.com/OEP/python-anyvcs into feature/fix-copy-cache
Merge branch 'develop' into feature/fix-copy-cache
PEP8-ify feature/fix-copy-cache from OEP
use path+nodeid for changeset lookup

this is for issue #40
Merge pull request #43 from OEP/feature/fix-copy-cache

use path+nodeid for changeset lookup
fix encoding errors for python3
Merge branch 'develop' into feature/fix-copy-cache
factor out and document anyvcs.probe()
add test for anyvcs.probe()
Merge branch 'develop' into feature/fix-copy-cache
factor out _get_repo_class
write anyvcs.clone()
write GitRepo.clone()
write clone unit test
write HgRepo.clone()
write SvnRepo.clone()
add anyvcs.clone() to documentation
fix GitRepo.ls() with reporting commits

Fix issue #40.  This gets rid of object caching for GitRepo.