installer (silent): optionally skip installation when files are in use

When the Git Bash is running, for example, Git for Windows cannot be
upgraded. Let's introduce a flag (/SKIPIFINUSE=1) that tells the installer
to please just exit, pretending to have succeeded, if we cannot upgrade
because files are in use. This flag only makes sense in silent
installation mode, of course, as the user would otherwise have a chance to
cancel the installation herself.

This option is also in effect when the installer was called from the VS
installer.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

installer/install.iss

@@ -581,6 +581,15 @@ begin
     end;
 end;
 
+procedure ExitProcess(uExitCode:Integer);
+external '[email protected] stdcall';
+
+procedure ExitEarlyWithSuccess();
+begin
+    DelTree(ExpandConstant('{tmp}'),True,True,True);
+    ExitProcess(0);
+end;
+
 function InitializeSetup:Boolean;
 var
     CurrentVersion,PreviousVersion:String;
@@ -1246,6 +1255,7 @@ function NextButtonClick(CurPageID:Integer):Boolean;
 var
     i:Integer;
     Version:TWindowsVersion;
+    Msg:String;
 begin
     // On a silent install, if your NextButtonClick function returns False
     // prior to installation starting, Setup will exit automatically.
@@ -1283,6 +1293,14 @@ begin
                 end;
 		    ;
             end else if not Processes[i].Restartable then begin
+	        if WizardSilent() and (ParamIsSet('SKIPIFINUSE') or ParamIsSet('VSNOTICE')) then begin
+		    Msg:='Skipping installation because the process '+Processes[i].Name+' (pid '+IntToStr(Processes[i].ID)+') is running, using Git for Windows'+#39+' files.';
+		    if ParamIsSet('SKIPIFINUSE') or (ExpandConstant('{log}')='') then
+		        LogError(Msg)
+		    else
+		        Log(Msg);
+		    ExitEarlyWithSuccess();
+		end;
                 SuppressibleMsgBox(
                     'Setup cannot continue until you close at least those applications in the list that are marked as "closing is required".'
                 ,   mbCriticalError