color: check if ui is already a subclass of colorui before wrapping it

since it's possible to reuse the ui object (see 80c599eee3f3)
between dispatch calls, the ui might have been wrapped already.

we could probably move this test up a bit but leaving it here
allows updates to take effect by extstyles() and configstyles().

hgext/color.py

@@ -349,8 +349,9 b' def uisetup(ui):'
         mode = _modesetup(ui_, opts)
         if mode:
             colorui._colormode = mode
-            colorui.__bases__ = (ui_.__class__,)
-            ui_.__class__ = colorui
+            if not issubclass(ui_.__class__, colorui):
+                colorui.__bases__ = (ui_.__class__,)
+                ui_.__class__ = colorui
             extstyles()
             configstyles(ui_)
         return orig(ui_, opts, cmd, cmdfunc)

tests/test-ui-color.py

@@ -1,4 +1,6 b''
+import os, sys
 from hgext import color
+from mercurial import dispatch, ui
 
 # ensure errors aren't buffered
 testui = color.colorui()
@@ -7,3 +9,25 b" testui.write('buffered\\n')"
 testui.warn('warning\n')
 testui.write_err('error\n')
 print repr(testui.popbuffer())
+
+# test dispatch.dispatch with the same ui object
+hgrc = open(os.environ["HGRCPATH"], 'w')
+hgrc.write('[extensions]\n')
+hgrc.write('color=\n')
+hgrc.close()
+
+ui_ = ui.ui()
+ui_.setconfig('ui', 'formatted', 'True')
+
+# call some arbitrary command just so we go through
+# color's wrapped _runcommand twice.
+# we're not interested in the output, so write that to devnull
+def runcmd():
+    sys.stdout = open(os.devnull, 'w')
+    dispatch.dispatch(dispatch.request(['version', '-q'], ui_))
+    sys.stdout = sys.__stdout__
+
+runcmd()
+print "colored? " + str(issubclass(ui_.__class__, color.colorui))
+runcmd()
+print "colored? " + str(issubclass(ui_.__class__, color.colorui))

tests/test-ui-color.py.out

@@ -1,3 +1,5 b''
 warning
 error
 'buffered\n'
+colored? True
+colored? True