For issue #4519, stop removing valid information from the EXTERNALS table
when calling 'svn upgrade'

* subversion/libsvn_client/upgrade.c
  (upgrade_externals_from_properties): New prototype.
  (svn_client_upgrade): Upgrade properly recorded wc-ng EXTERNALS directly. Only
    if there are none, try to upgrade from svn:externals. Extract this upgrade code
    to a separate function upgrade_externals_from_properties().
  (upgrade_externals_from_properties): New function.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1625533 13f79535-47bb-0310-9956-ffa450edef68
* subversion/libsvn_client/upgrade.c
  (upgrade_externals_from_properties): Remove doubled ';', which
    caused C89/C90 warnings in gcc and Visual C++.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1625537 13f79535-47bb-0310-9956-ffa450edef68