commands: make "hg import" use dirstateguard only for --no-commit

Previous patch made dirstate changes in a transaction scope "all or
nothing". Therefore, 'dirstateguard' is meaningless, if its scope is
as same as one of the related transaction.

Before this patch, "hg import" uses 'dirstateguard' always, but
transaction is also started if '--no-commit' isn't specified.

To avoid redundancy, this patch makes "hg import" use dirstateguard
only if transaction isn't started (= '--no-commit' is specified).

In this patch, 'if dsguard' can be examined safely, because 'dsguard'
is initialized (with None) before outermost 'try'.

mercurial/commands.py

@@ -4407,10 +4407,11 b' def import_(ui, repo, patch1=None, *patc'
     try:
         try:
             wlock = repo.wlock()
-            dsguard = cmdutil.dirstateguard(repo, 'import')
             if not opts.get('no_commit'):
                 lock = repo.lock()
                 tr = repo.transaction('import')
+            else:
+                dsguard = cmdutil.dirstateguard(repo, 'import')
             parents = repo.parents()
             for patchurl in patches:
                 if patchurl == '-':
@@ -4448,7 +4449,8 b' def import_(ui, repo, patch1=None, *patc'
                 tr.close()
             if msgs:
                 repo.savecommitmessage('\n* * *\n'.join(msgs))
-            dsguard.close()
+            if dsguard:
+                dsguard.close()
             return ret
         finally:
             # TODO: get rid of this meaningless try/finally enclosing.