ignore configuration files under netbeans control for each user

.gitignore

  ~$3500NetworkedGraphicsSyllabus2019JulySeptember.doc
+/nbproject/build-impl.xml~
+/nbproject/genfiles.properties
 /nbproject/private/
 /assignments/build/
 /assignments/dist/
+/assignments/nbproject/build-impl.xml~
 /assignments/nbproject/genfiles.properties
 /assignments/nbproject/private/
 /examples/manifest.mf
 /examples/build/
 /examples/dist/
+/examples/nbproject/build-impl.xml~
 /examples/nbproject/genfiles.properties
 /examples/nbproject/private/
 /specifications/*.SAVEME
@@ -21,4 +25,3 @@
 /specifications/RPR*.xml
 /specifications/SISO*.xml
 /specifications/archive
-/assignments/nbproject/build-impl.xml~