Add convenience methods for checking whether an ExecRes failed or succeeded. Split up GitWrapper#failed.

core.quotePath and core.precomposeUnicode should remove unicode related problems caused by having to unquote paths

return an Optional<List> from getMergeCommits() as an empty Optional indicates failure whereas an empty List indicates absence of merge commits, store SUMMARY and BOUNDARY header fields in the 'other' Map

Return the actual name of the commit from its getId() function, this way Repository#checkout(Reference) will bring one 'on the branch' if the given Reference is a Branch.

differentiate between failure modes in the logging done in importRepository(), try and use the canonical file path for the URL as a fallback

String equals may be faster than Repository equals, id should never be null and returning "null" doesn't seem useful...

correctly parse the message (by finding the first empty line in the cat-file output and taking the rest of it as the message)
use a very evil trick to avoid the Matcher initialization cost when parsing is unnecessary due to the fields already being initialized

Document ExecRes and add methods for getting the trimmed output (that use a lazily initialized field). Use the method for getting the trimmed output everywhere it seems necessary. Only initialize author / committer info in the getCommitInfo() method if they are null.