print more information for tests

- OK or FAIL
- exception message (traceback) for failures
- test duration (in ms)
add implementation notes to dmain2.d
remove unused global variable
Merge pull request #577 from WalterBright/rm-unused-global

remove unused global variable
refactor src/rt/minfo.d
Merge pull request #568 from dawgfoto/betterTestRunner

print more information for tests
Merge pull request #575 from WalterBright/add-dll-notes

add implementation notes to dmain2.d
Merge pull request #578 from WalterBright/refactor-minfo

refactor src/rt/minfo.d