update copyright year to range
Only clean GEM_ENV/GEM_HOME when actually needed.

See #2915 for more information.
Detect tools before cleaning in ./configure

Previously this script would first try to run `ruby -S rake clean`. The `rake`
command here was pulled from the `@rake` instance variable. Due to this
variable not being set by default at this point the resulting command would be
`ruby -S clean` instead, resulting in a load error.

This commit fixes this by first checking the tools used and *then* running a
clean.

This fixes #2915.
Added specs on main#define_method.
Added main#define_method.
Merge pull request #2921 from razielgn/main-define_method

Added main#define_method.
Merge pull request #2918 from gdi2290/patch-1

update copyright year to range
Mention contributors in the LICENSE file.

This was added after being suggested by @brixen and approved by @evanphx.
Add dates to changelog
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
Added failing spec for BasicObject::BasicObject.

This was added as a starting point for #2828.
Changed description of failing BasicObject spec.