ruby 1.8.7 doesn't ship with rdoc. make it a development dependency.
fixed method elimination test to work under 1.8.7
make process_time_test succeed under 1.8.7
fix pause_resume test under 1.8.7
clean OS X build artifacts
refactored code for enabling/disabling gc_stats
fixed GC_TIME measurement
fixed GC_RUNS test
fixed memory measurement test
reenable gc_stats toggling for now.

not sure we want to keep this, but at least it's now consistent with older ruby-profs.
1.8.7 doesn't support gem command out of the box
make testing the default rake task.

99.99% of all gems have the test task as the default in their top Rakefile.
chmod 755 bin/ruby-prof
removed unused variable to eliminate C compiler warning