[MSVC] allow user level project customization

Author: NicolasDorier

build_msvc/common.init.vcxproj

@@ -115,4 +115,5 @@
       <AdditionalDependencies>crypt32.lib;Iphlpapi.lib;ws2_32.lib;Shlwapi.lib;kernel32.lib;user32.lib;gdi32.lib;winspool.lib;comdlg32.lib;advapi32.lib;shell32.lib;ole32.lib;oleaut32.lib;uuid.lib;odbc32.lib;odbccp32.lib;%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
   </ItemDefinitionGroup>
+  <Import Project="common.init.vcxproj.user" Condition="Exists('common.init.vcxproj.user')" />
 </Project>