add --resume option to osm import-history
reuse FindTreeChild command while looking for way nodes
prepare FindTreeChild with current head tree to avoid multiple lookups
Do not load all buckets to compute the final tree size/num trees.

RevTreeBuilder.normalizeToBuckets() performance optimization to avoid loading all the
buckets that compose the tree unnecessarily to compute the final tree size and number
of subtrees, but instead pre compute the deltas out of the changed buckets only.
do now swallow exception in ImportOp
Initial RevertOp implementation.
Added initial unit tests for revert.
Fleshed out revert implementation

Added more unit tests
Basic cli command
Functional tests
Man pages
Fixed issues with empty type trees

Fixed an issue which caused empty trees to not import.
Fixed an issue which caused commit to not move the feature type of an empty tree to the object database.
Merge remote-tracking branch 'jdgarrett/revert'
Updated unit tests and implemented rev-parse type verification
Merge remote-tracking branch 'jdgarrett/EmptyTrees' into mergeme