run merge program in repo root.

run merge program in repo root.
before, merge program was run in user current directory.  Well defined
location is better for scripts.  no more need to pass HG_ROOT to merge
program now.

--- a/hgmerge	Fri Mar 10 23:34:36 2006 -0800
+++ b/hgmerge	Sat Mar 11 21:33:19 2006 -0800
@@ -3,10 +3,10 @@
 # hgmerge - default merge helper for Mercurial
 #
 # This tries to find a way to do three-way merge on the current system.
-# The result ought to end up in $1.
+# The result ought to end up in $1.  Script is run in root directory of
+# repository.
 #
 # Environment variables set by Mercurial:
-# HG_ROOT            repo root
 # HG_FILE            name of file within repo
 # HG_MY_NODE         revision being merged
 # HG_OTHER_NODE      revision being merged

--- a/mercurial/localrepo.py	Fri Mar 10 23:34:36 2006 -0800
+++ b/mercurial/localrepo.py	Sat Mar 11 21:33:19 2006 -0800
@@ -1702,9 +1702,8 @@
 
         cmd = (os.environ.get("HGMERGE") or self.ui.config("ui", "merge")
                or "hgmerge")
-        r = util.system('%s "%s" "%s" "%s"' % (cmd, a, b, c),
-                        environ={'HG_ROOT': self.root,
-                                 'HG_FILE': fn,
+        r = util.system('%s "%s" "%s" "%s"' % (cmd, a, b, c), cwd=self.root,
+                        environ={'HG_FILE': fn,
                                  'HG_MY_NODE': p1,
                                  'HG_OTHER_NODE': p2,
                                  'HG_FILE_MY_NODE': hex(my),