The "common.h" should be included before "config.h".

When building libgit2 for ia32 architecture on a x64 machine, including
"config.h" without a "common.h" would result the following error:
C:\Program Files\Microsoft SDKs\Windows\v7.1\include\winbase.h(2288): error C2373: 'InterlockedIncrement' : redefinition; different type modifiers [C:\cygwin\home\zcbenz\codes\git-utils\build\libgit2.vcxproj]
C:\Program Files\Microsoft SDKs\Windows\v7.1\include\winbase.h(2295): error C2373: 'InterlockedDecrement' : redefinition; different type modifiers [C:\cygwin\home\zcbenz\codes\git-utils\build\libgit2.vcxproj]
C:\Program Files\Microsoft SDKs\Windows\v7.1\include\winbase.h(2303): error C2373: 'InterlockedExchange' : redefinition; different type modifiers [C:\cygwin\home\zcbenz\codes\git-utils\build\libgit2.vcxproj]
C:\Program Files\Microsoft SDKs\Windows\v7.1\include\winbase.h(2314): error C2373: 'InterlockedExchangeAdd' : redefinition; different type modifiers [C:\cygwin\home\zcbenz\codes\git-utils\build\libgit2.vcxproj]

src/attr.c

+#include "common.h"
 #include "repository.h"
 #include "fileops.h"
 #include "config.h"

src/ignore.c

 #include "git2/ignore.h"
+#include "common.h"
 #include "ignore.h"
 #include "attr.h"
 #include "path.h"

src/remote.c

@@ -10,6 +10,7 @@
 #include "git2/oid.h"
 #include "git2/net.h"
 
+#include "common.h"
 #include "config.h"
 #include "repository.h"
 #include "remote.h"