Log Message:
Update to 2.3.1:

clone: don't fail with --update for non-local clones (issue3578)
commit: normalize filenames when checking explicit files (issue3576)
fileset: actually implement 'minusset'
fileset: do not traceback on invalid grep pattern
fileset: exclude deleted files from matchctx.existing()
fileset: fix generator vs list bug in fast path
fileset: matchctx.existing() must consider ignored files
fileset: matchctx.existing() must consider unknown files
largefiles: adjust localstore to handle batch statlfile requests (issue3583)
merge: handle case when heads are all bookmarks
obsolete: import modules within mercurial/ without "from mercurial"
revlog: don't try to partialmatch strings those length > 40
rollback: write dirstate branch with correct encoding
store: only one kind of OSError means "nonexistent entry"
store: sort the results of fncachestore.datafiles()
strip: fix revset usage (issue3604)
templater: handle a missing value correctly
verify: do not choke on valid changelog without manifest
wix: bump MSI based installers to use Python 2.7