Use a global lock for reading/writing any index file. Possible
bottleneck, but good enough for now.
Don't create a mailbox directory until a message is being written to it.
- Removed extra message object from ReadBody() return type
- We now use enmime's GetHeader() when building the GOB, this will get
us alternate character set decoding for the From and Subject headers.
- Added a swaks test with a utf-8 subject line
Logging methods were renamed so they don't trigger go-vet warnings for
error() and Error() formatting.
Unit tests were updated to use new github.com/stretchr repo (was renamed
from stretchrcom)
Missing methods were added to Message mock object.
