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Remove unused -Xthread.debug option

Debugging information for threads is set at compile time
not runtime. This patch removes the unused -Xthread.debug option
along with two redundant messages that were already controlled
by the cDebugThreading variable set at compile time.
Merge pull request #2924 from southerngs/remove_thread_debug

Remove unused -Xthread.debug option
Added other standard lib gems.
Added spec for #require of .rb vs .<dlext>.
Removed config_version hackery.
Fixed #require to load .rb before c-ext.
Reworked requiring pre-installed gems.
Ignore rake clean if not configured.
Merge pull request #2922 from sandstrom/patch-1

Add dates to change log