Add Microsoft Visual Studio 2017 support to our build scripting.

* gen-make.py
  (_usage_exit): Document new support.
  
* build/generator/gen_win_dependencies.py
  (parse_options): Add '2017' as explicitly handled option.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1786653 13f79535-47bb-0310-9956-ffa450edef68

build/generator/gen_win_dependencies.py

@@ -259,6 +259,11 @@ def parse_options(self, options):
           self.sln_version = '12.00'
           self.vcproj_version = '14.0'
           self.vcproj_extension = '.vcxproj'
+        elif val == '2017' or val == '15':
+          self.vs_version = '2015'
+          self.sln_version = '12.00'
+          self.vcproj_version = '15.0'
+          self.vcproj_extension = '.vcxproj'
         elif re.match('^20\d+$', val):
           print('WARNING: Unknown VS.NET version "%s",'
                 ' assuming VS2012. Your VS can probably upgrade')

gen-make.py

@@ -206,7 +206,7 @@ def _usage_exit(err=None):
   print("           Use static openssl")
   print("")
   print("  --vsnet-version=VER")
-  print("           generate for VS.NET version VER (2005-2015 or 9.0-14.0)")
+  print("           generate for VS.NET version VER (2005-2017 or 9.0-15.0)")
   print("           [implies '-t vcproj']")
   print("")
   print(" -D NAME[=value]")