updated to current Cygwin, after 2.10.0-1 from 02-Feb-2018;
record cygwin mirror explicitly;

--- a/Admin/PLATFORMS	Mon Jun 04 14:21:16 2018 +0200
+++ b/Admin/PLATFORMS	Mon Jun 04 21:57:38 2018 +0200
@@ -39,7 +39,7 @@
                     macOS 10.13 High Sierra
 
   x86_64-windows    Windows 7
-  x86_64-cygwin     Cygwin 2.8 http://isabelle.in.tum.de/cygwin_2017 (x86_64/release)
+  x86_64-cygwin     Cygwin 2.10 https://isabelle.sketis.net/cygwin_2018 (x86_64/release)
 
 All of the above platforms are 100% supported by Isabelle -- end-users
 should not have to care about the differences (at least in theory).

--- a/Admin/Windows/Cygwin/Cygwin-Setup.bat	Mon Jun 04 14:21:16 2018 +0200
+++ b/Admin/Windows/Cygwin/Cygwin-Setup.bat	Mon Jun 04 21:57:38 2018 +0200
@@ -1,3 +1,3 @@
 @echo off
 
-"%CD%\contrib\cygwin\isabelle\cygwin" --site http://isabelle.in.tum.de/cygwin_2017 --no-verify --only-site --local-package-dir "%TEMP%" --root "%CD%\contrib\cygwin"
+"%CD%\contrib\cygwin\isabelle\cygwin" --site https://isabelle.sketis.net/cygwin_2018 --no-verify --only-site --local-package-dir "%TEMP%" --root "%CD%\contrib\cygwin"

--- a/Admin/Windows/Cygwin/README	Mon Jun 04 14:21:16 2018 +0200
+++ b/Admin/Windows/Cygwin/README	Mon Jun 04 21:57:38 2018 +0200
@@ -1,10 +1,10 @@
 Cygwin
 ======
 
-* http://www.cygwin.com/
+* https://www.cygwin.com/
 
 * Mirror with many old versions (not setup.ini)
-  http://ftp.eq.uc.pt/software/pc/prog/cygwin
+  https://ftp.eq.uc.pt/software/pc/prog/cygwin
 
 * Local snapshots:
   http://isabelle.in.tum.de/cygwin  (Isabelle2012)
@@ -15,6 +15,7 @@
   http://isabelle.in.tum.de/cygwin_2016  (Isabelle2016)
   http://isabelle.in.tum.de/cygwin_2016-1  (Isabelle2016-1)
   http://isabelle.in.tum.de/cygwin_2017  (Isabelle2017)
+  https://isabelle.sketis.net/cygwin_2018  (Isabelle2018)
 
 * Apache2 redirects for virtual host isabelle.conf:
   Redirect /cygwin/release http://ftp.eq.uc.pt/software/pc/prog/cygwin/release
@@ -31,6 +32,9 @@
   Redirect /cygwin_2017/x86/release http://ftp.eq.uc.pt/software/pc/prog/cygwin/x86/release
   Redirect /cygwin_2017/x86_64/release http://ftp.eq.uc.pt/software/pc/prog/cygwin/x86_64/release
   Redirect /cygwin_2017/noarch/release http://ftp.eq.uc.pt/software/pc/prog/cygwin/noarch/release
+  Redirect /cygwin_2018/x86/release https://ftp.eq.uc.pt/software/pc/prog/cygwin/x86/release
+  Redirect /cygwin_2018/x86_64/release https://ftp.eq.uc.pt/software/pc/prog/cygwin/x86_64/release
+  Redirect /cygwin_2018/noarch/release https://ftp.eq.uc.pt/software/pc/prog/cygwin/noarch/release
 
 * Quasi-component: "isabelle build_cygwin" (as Administrator)
 

--- a/Admin/components/bundled-windows	Mon Jun 04 14:21:16 2018 +0200
+++ b/Admin/components/bundled-windows	Mon Jun 04 21:57:38 2018 +0200
@@ -1,3 +1,3 @@
 #additional components to be bundled for release
-cygwin-20170930
+cygwin-20180604
 windows_app-20180417

--- a/Admin/components/components.sha1	Mon Jun 04 14:21:16 2018 +0200
+++ b/Admin/components/components.sha1	Mon Jun 04 21:57:38 2018 +0200
@@ -37,6 +37,7 @@
 d9ad7aae99d54e3b9813151712eb88a441613f04  cygwin-20161024.tar.gz
 f8eb6a0f722e3cfe3775d1204c5c7063ee1f008e  cygwin-20170828.tar.gz
 c22048912b010a5a0b4f2a3eb4d318d6953761e4  cygwin-20170930.tar.gz
+5a3919e665947b820fd7f57787280c7512be3782  cygwin-20180604.tar.gz
 0fe549949a025d65d52d6deca30554de8fca3b6e  e-1.5.tar.gz
 2e293256a134eb8e5b1a283361b15eb812fbfbf1  e-1.6-1.tar.gz
 e1919e72416cbd7ac8de5455caba8901acc7b44d  e-1.6-2.tar.gz

--- a/src/Pure/Admin/build_cygwin.scala	Mon Jun 04 14:21:16 2018 +0200
+++ b/src/Pure/Admin/build_cygwin.scala	Mon Jun 04 21:57:38 2018 +0200
@@ -9,7 +9,7 @@
 
 object Build_Cygwin
 {
-  val default_mirror: String = "http://isabelle.in.tum.de/cygwin_2017"
+  val default_mirror: String = "https://isabelle.sketis.net/cygwin_2018"
 
   val packages: List[String] =
     List("curl", "nano", "perl", "perl-libwww-perl", "rlwrap", "unzip")
@@ -33,6 +33,8 @@
           try { Bytes.read(Url(cygwin_exe_name)) }
           catch { case ERROR(_) => error("Failed to download " + quote(cygwin_exe_name)) })
 
+        File.write(cygwin_isabelle + Path.explode("cygwin_mirror"), mirror)
+
         Isabelle_System.bash(
           "chmod +x " + File.bash_path(cygwin_exe) + " && " +
           File.bash_path(cygwin_exe) + " -h </dev/null >/dev/null").check