[sdb] Add support for DebuggerNonUserCodeAttribute.
Disable bug-18026.exe when running tests in the CI environment

The test performed in bug-18026.exe can sometimes fail if the hazard
table gets full. Disabling it in CI testing avoids unwanted noise.

See https://bugzilla.xamarin.com/show_bug.cgi?id=19235
Try again to get TravisCI to work
Verbose testing
Hopefully working TravisCI build
Respect TEST_TARGET setting
Fix runtime checking
Cleanup
Test compiler & fix 3.5, 12
Try building tests before running them