[Bug #19969] Compact st_table after deleted if possible

	---
	 hash.c                 | 19 +++++++++++++++++++
	 st.c                   | 40 +++++++++++++++++++++++++++++-----------
	 test/ruby/test_hash.rb |  9 +++++++++
	 3 files changed, 57 insertions(+), 11 deletions(-)