Update sources.cfg to use maintenance branches. (#1099)

I created most of these branches myself today, with as starting point the master branches before the recent updates to drop Python 2.7.

sources.cfg

@@ -18,16 +18,16 @@ zope.globalrequest = git ${remotes:github}/zope.globalrequest pushurl=${remotes:
 ZODB = git ${remotes:github}/ZODB pushurl=${remotes:github_push}/ZODB
 
 # Optional dependencies
-five.localsitemanager = git ${remotes:github}/five.localsitemanager pushurl=${remotes:github_push}/five.localsitemanager
+five.localsitemanager = git ${remotes:github}/five.localsitemanager pushurl=${remotes:github_push}/five.localsitemanager branch=3.x
 Missing = git ${remotes:github}/Missing pushurl=${remotes:github_push}/Missing
-Products.BTreeFolder2 = git ${remotes:github}/Products.BTreeFolder2 pushurl=${remotes:github_push}/Products.BTreeFolder2
-Products.MailHost = git ${remotes:github}/Products.MailHost pushurl=${remotes:github_push}/Products.MailHost
-Products.PythonScripts = git ${remotes:github}/Products.PythonScripts pushurl=${remotes:github_push}/Products.PythonScripts
+Products.BTreeFolder2 = git ${remotes:github}/Products.BTreeFolder2 pushurl=${remotes:github_push}/Products.BTreeFolder2 branch=4.x
+Products.MailHost = git ${remotes:github}/Products.MailHost pushurl=${remotes:github_push}/Products.MailHost branch=4.x
+Products.PythonScripts = git ${remotes:github}/Products.PythonScripts pushurl=${remotes:github_push}/Products.PythonScripts branch=4.x
 Products.ZCatalog = git ${remotes:github}/Products.ZCatalog pushurl=${remotes:github_push}/Products.ZCatalog branch=5.x
-Products.Sessions = git ${remotes:github}/Products.Sessions pushurl=${remotes:github_push}/Products.Sessions
-Products.TemporaryFolder = git ${remotes:github}/Products.TemporaryFolder pushurl=${remotes:github_push}/Products.TemporaryFolder
-Products.ZODBMountPoint = git ${remotes:github}/Products.ZODBMountPoint pushurl=${remotes:github_push}/Products.ZODBMountPoint
-Products.SiteErrorLog = git ${remotes:github}/Products.SiteErrorLog pushurl=${remotes:github_push}/Products.SiteErrorLog
+Products.Sessions = git ${remotes:github}/Products.Sessions pushurl=${remotes:github_push}/Products.Sessions branch=4.x
+Products.TemporaryFolder = git ${remotes:github}/Products.TemporaryFolder pushurl=${remotes:github_push}/Products.TemporaryFolder branch=6.x
+Products.ZODBMountPoint = git ${remotes:github}/Products.ZODBMountPoint pushurl=${remotes:github_push}/Products.ZODBMountPoint branch=1.x
+Products.SiteErrorLog = git ${remotes:github}/Products.SiteErrorLog pushurl=${remotes:github_push}/Products.SiteErrorLog branch=5.x
 Record = git ${remotes:github}/Record pushurl=${remotes:github_push}/Record
 ZServer = git ${remotes:github}/ZServer pushurl=${remotes:github_push}/ZServer
 
@@ -49,7 +49,7 @@ zope.exceptions = git ${remotes:github}/zope.exceptions
 zope.filerepresentation = git ${remotes:github}/zope.filerepresentation
 zope.i18n = git ${remotes:github}/zope.i18n
 zope.i18nmessageid = git ${remotes:github}/zope.i18nmessageid
-zope.interface = git ${remotes:github}/zope.interface
+zope.interface = git ${remotes:github}/zope.interface branch=5.x
 zope.lifecycleevent = git ${remotes:github}/zope.lifecycleevent
 zope.location = git ${remotes:github}/zope.location
 zope.pagetemplate = git ${remotes:github}/zope.pagetemplate