Preserve AppVeyor original build number for assembly patching

appveyor.yml

@@ -23,8 +23,8 @@ install:
 assembly_info:
   patch: true
   file: '**\AssemblyInfo.*'
-  assembly_version: '$(appveyor_version)'
-  assembly_file_version: '$(appveyor_version)'
+  assembly_version: '$(ms_file_version)'
+  assembly_file_version: '$(ms_file_version)'
   assembly_informational_version: '$(mssemver)'
 
 before_build:

build/appveyor-semver.ps1

@@ -10,6 +10,7 @@ $appveyor_version = $mssemver
 $Env:semver = $semver
 $Env:mssemver = $mssemver
 $Env:appveyor_version = $appveyor_version
+$Env:ms_file_version = $version.ToString()
 
 "Envrionment variable 'semver' set:" + $Env:semver
 "Envrionment variable 'mssemver' set:" + $Env:mssemver