config: register the 'devel.strip-obsmarkers' config

The single explicit default that existed so far is converted to registered
config value.

mercurial/configitems.py

@@ -80,6 +80,9 b" coreconfigitem('devel', 'serverexactprot"
 coreconfigitem('devel', 'serverrequirecert',
     default=None,
 )
+coreconfigitem('devel', 'strip-obsmarkers',
+    default=True,
+)
 coreconfigitem('patch', 'fuzz',
     default=2,
 )

mercurial/repair.py

@@ -132,7 +132,7 b' def strip(ui, repo, nodelist, backup=Tru'
     stripbases = [cl.node(r) for r in tostrip]
 
     stripobsidx = obsmarkers = ()
-    if repo.ui.configbool('devel', 'strip-obsmarkers', True):
+    if repo.ui.configbool('devel', 'strip-obsmarkers'):
         obsmarkers = obsutil.exclusivemarkers(repo, stripbases)
     if obsmarkers:
         stripobsidx = [i for i, m in enumerate(repo.obsstore)