Enable per-thread errno on Solaris
Remove unused Thread.sm_clen variable.

It stored the size of the global context list, but that isn't used
explicitly anywhere.
Added comment for -D_REENTRANT
Merge pull request #862 from klickverbot/remove-sm_clen

Remove unused Thread.sm_clen variable.
Merge pull request #860 from jasonbking/errno

Enable per-thread errno on Solaris