Fixes CORE-1987 "mvn liquibase:diff" does not find any differences between databases

Fix empty schemaComparison
Bug fix CORE-1745
CORE-2042 If liquibase.jar is nested in another jar/war/ear, it fails to start with a "cannot find implementation of liquibase.logging.Logger" error
Merge pull request #309 from mrorat/CORE-1745-afterColumn_not_working_in_MySQL

Bug fix CORE-1745
Merge pull request #291 from deniedboarding/CORE-1987

Fixes CORE-1987
Fixes CORE-1987 "mvn liquibase:diff" does not find any differences between databases

Fix empty schemaComparison
(cherry picked from commit efce4fe)
If a command fails in dropAll, continue on.
Merge remote-tracking branch 'origin/master'
Merge branch '3.2.x'