installer: switch the libcurl default to Secure Channel

In line with git-for-windows/MINGW-packages#76,
the default SSL/TLS backend is now the Secure Channel one.

Let's reflect that in the installer.

This makes Git for Windows' maintenance easier (see
git-for-windows/git#4350 for a fuller
explanation). But it has further benefits: the Secure Channel backend
is the "more native" choice on Windows, as it integrates better with
Windows. For example, when trusting a host with a self-signed
certificate in a web browser, that trust extends to Secure Channel. With
the OpenSSL backend, users had to jump through manual hoops to get `git
clone <url>` to trust a host with a self-signed certificate.

Note: The installer will _still_ pick up previous choices when upgrading
from an earlier Git for Windows version. Only fresh installs without any
current Git for Windows installations will receive the new default.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

installer/install.iss

@@ -2212,7 +2212,7 @@ begin
         'OpenSSL': RdbCurlVariant[GC_OpenSSL].Checked:=True;
         'WinSSL': RdbCurlVariant[GC_WinSSL].Checked:=True;
     else
-        RdbCurlVariant[GC_OpenSSL].Checked:=True;
+        RdbCurlVariant[GC_WinSSL].Checked:=True;
     end;
 
     (*
@@ -3536,9 +3536,9 @@ begin
     RecordChoice(PreviousDataKey,'Tortoise Option',Data2);
 
     // HTTPS implementation (cURL) options.
-    Data:='OpenSSL';
-    if RdbCurlVariant[GC_WinSSL].Checked then begin
-        Data:='WinSSL';
+    Data:='WinSSL';
+    if RdbCurlVariant[GC_OpenSSL].Checked then begin
+        Data:='OpenSSL';
     end;
     RecordChoice(PreviousDataKey,'CURL Option',Data);