Increase the specificity of PlayFramework rules

The original ignore was far too general and results in eliminating packages
named "db" or "project", for example. These are not that uncommon for package
names. Fixes #921.

PlayFramework.gitignore

 # Ignore Play! working directory #
-bin
-db
-eclipse
-lib
-log
-logs
-modules
-precompiled
-project/project
-project/target
-target
-tmp
+bin/
+/db
+.eclipse
+/lib/
+/logs/
+/modules
+/project/project
+/project/target
+/target
+tmp/
 test-result
 server.pid
 *.iml
 *.eml
-dist
+/dist/
 .cache