6909462: Fix nbproject/private references in .hgignore

Summary: See bugzilla issue 100097
Reviewed-by: tbell
Contributed-by: NJesse Glick <jesse.glick@sun.com>

.hgignore

 ^build/
 ^dist/
-^nbproject/private/
+/nbproject/private/
 ^src/share/tools/hsdis/build/
 ^src/share/tools/IdealGraphVisualizer/[a-zA-Z0-9]*/build/
 ^src/share/tools/IdealGraphVisualizer/build/