Merge branch 'jk/fix-alias-pager-config-key-warnings' into maint

Because the configuration system does not allow "alias.0foo" and "pager.0foo" as the configuration key, the user cannot use '0foo' as a custom command name anyway, but "git 0foo" tried to look these keys up and emitted useless warnings before saying '0foo is not a git command'. These warning messages have been squelched. * jk/fix-alias-pager-config-key-warnings: config: silence warnings for command names with invalid keys