Make coinmp build with VS2013

Add a patch to mangle the project files a bit so that they work better
on a machine with only VS2013 installed. At least in my case. But why
we still need to *also* have those /p:PlatformToolset=v120
/p:VisualStudioVersion=12.0 in the ExternalProject_coinmp.mk I don't
know.

Change-Id: Ieebd729c3ba89cf22231fb943f3739d6be5c7acd