Paring back the scope of our shared .gitignore

Importantly, limit the exclusion of build.properties
to the file in the root directory, paving the way for
the return of an SBT build.

  - Unignores .bak, .jar, and ~
  - limit ignorance of qbin to the root directory

.log files, generated by partest, are still ignored.

To see ignored files in your workspace, try:

    git ls-files --others --ignored --exclude-standard -- test | grep log
    git status --ignored -- test

Review by @paulp