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

.gitignore

@@ -9,10 +9,21 @@
 # see also test/files/.gitignore
 #
 
-*.jar
-*~
+#
+# JARs aren't checked in, they are fetched by Ant / pull_binary_libs.sh
+#
+# We could be more concise with /lib/**/*.jar but that assumes
+# a late-model git.
+#
+/lib/ant/*.jar
+/lib/*.jar
+/test/files/codelib/*.jar
+/test/files/lib/*.jar
+/test/files/speclib/instrumented.jar
+/tools/*.jar
 
-build.properties
+# Developer specific Ant properties
+/build.properties
 
 # target directories for ant build
 /build/
@@ -33,11 +44,5 @@ build.properties
 /.idea
 /.settings
 
-# bak files produced by ./cleanup-commit
-*.bak
-
 # Standard symbolic link to build/quick/bin
-qbin
-
-# Mac specific, but that is common enough a dev platform to warrant inclusion.
-.DS_Store
+/qbin