Fix Rational(== 0)#** with negative Rational
Merge pull request #2531 from kachick/fix-rational-exponent

Fix Rational(== 0)#** with negative Rational
Fix spec context for Time#inspect
Add a spec for Time#{to_s,inspect} encoding
Fix Time#{to_s,inspect} encoding for 2.0
Fixed misbehaving exec and spawn specs.

Don't ever, ever write to anything but a tmp() directory or file.
Merge pull request #2532 from kachick/2.0-time-to_s

Time#{to_s,inspect} should return US-ASCII encoded String from 2.0
Add spec on EncodingConverter#primitive_convert on clearing the source buffer.
Fix EncodingConverter#primitive_convert: clear source buffer if exists.
Update existing usage of EncodingConverter#primitive_convert after fixes.