Fix deprecation comment on clear.

It doesn't follow the format that those comments normally take, and the
date isn't good, because while it was committed in March of 2014, it
wasn't actually get released until mid-August with 2.066, and it really
needs to be deprecated for _at least_ 6 months, if not longer, before
we remove it.
Merge pull request #1004 from jmdavis/clear

Fix deprecation comment on clear.
use MonoTime/Duration instead of clock() for higher precision when profiling the GC
also fix building with PRINTF_TO_FILE
Merge pull request #1005 from rainers/gc_profile_ticks

use MonoTime/Duration instead of clock() for higher precision when profiling the GC