Require Mercurial on PATH when building a Windows release.
Without it, we will generate invalid build information for sys.version
diff --git a/Tools/msi/buildrelease.bat b/Tools/msi/buildrelease.bat
index b39f13e..d441250 100644
--- a/Tools/msi/buildrelease.bat
+++ b/Tools/msi/buildrelease.bat
@@ -44,6 +44,9 @@
if errorlevel 1 goto :eof
:skipdoc
+where hg >nul 2>nul
+if errorlevel 1 echo Cannot find hg on PATH & exit /B 1
+
where dlltool 2>nul >"%TEMP%\dlltool.loc"
if errorlevel 1 dir "%D%..\..\externals\dlltool.exe" /s/b > "%TEMP%\dlltool.loc"
if errorlevel 1 echo Cannot find binutils on PATH or in externals & exit /B 1