pager: skip uisetup if chg is detected

chg has its own pager implementation that it wants to skip pager's uisetup.
It is currently done by redirecting stdout to /dev/null, which has unintended
side effects. This patch makes pager aware of chg and skip uisetup directly
from pager. We may want to merge chg and pager's pager implementation to
make this unnecessary in the future.

hgext/pager.py

@@ -117,6 +117,11 b' def uisetup(ui):'
     if '--debugger' in sys.argv or not ui.formatted():
         return
 
+    # chg has its own pager implementation
+    argv = sys.argv[:]
+    if 'chgunix' in dispatch._earlygetopt(['--cmdserver'], argv):
+        return
+
     def pagecmd(orig, ui, options, cmd, cmdfunc):
         p = ui.config("pager", "pager", os.environ.get("PAGER"))
         usepager = False