Fix _wt_epoch

Cleanup SConstruct, and add more details to os_open errors
Merge pull request #1289 from markbenvenuto/epoch_fix

Fix _wt_epoch
Match changes in Win, mention the system call name.
update
Change linked CRT default.

Statically linked CRT is now the default.
Dynamically linked CRT is an option.
Merge pull request #1290 from markbenvenuto/static_crt

Change linked CRT default.