Write out hgrc properly.

Write out hgrc properly.
Previously, we simply appended to the hgrc file, which meant that it
ended up containing multiple "paths" sections.  Now, we only modify
"paths.default".

--- a/mercurial/commands.py	Sun Sep 04 15:12:20 2005 -0700
+++ b/mercurial/commands.py	Sun Sep 04 15:47:59 2005 -0700
@@ -10,7 +10,7 @@
 demandload(globals(), "os re sys signal shutil imp")
 demandload(globals(), "fancyopts ui hg util lock revlog")
 demandload(globals(), "fnmatch hgweb mdiff random signal time traceback")
-demandload(globals(), "errno socket version struct atexit sets")
+demandload(globals(), "ConfigParser errno socket version struct atexit sets")
 
 class UnknownCommand(Exception):
     """Exception raised if command is not in the command table."""
@@ -622,9 +622,16 @@
         repo = hg.repository(ui, dest, create=1)
         repo.pull(other)
 
-    f = repo.opener("hgrc", "a")
-    f.write("\n[paths]\n")
-    f.write("default = %s\n" % abspath)
+    cfg = ConfigParser.SafeConfigParser()
+    try:
+        fp = repo.opener('hgrc', 'r')
+        os.unlink(fp.name)
+        cfg.readfp(fp)
+    except IOError, inst:
+        if inst.errno != errno.ENOENT: raise
+    if not cfg.has_section('paths'): cfg.add_section('paths')
+    cfg.set('paths', 'default', abspath)
+    cfg.write(repo.opener('hgrc', 'w'))
 
     if not opts['noupdate']:
         update(ui, repo)