Add optional BEFORE param to INCLUDE_DIRECTORIES so that include dirs can be specified before the actual include dirs

Source/cmIncludeDirectoryCommand.cxx

@@ -48,10 +48,19 @@ bool cmIncludeDirectoryCommand::InitialPass(std::vector<std::string> const& args
     this->SetError("called with incorrect number of arguments");
     return false;
     }
-  for(std::vector<std::string>::const_iterator i = args.begin();
-      i != args.end(); ++i)
+
+  std::vector<std::string>::const_iterator i = args.begin();
+
+  bool before = false;
+  if ((*i) == "BEFORE")
     {
-    m_Makefile->AddIncludeDirectory((*i).c_str());
+    before = true;
+    ++i;
+    }
+
+  for(; i != args.end(); ++i)
+    {
+    m_Makefile->AddIncludeDirectory((*i).c_str(), before);
     }
   return true;
 }

Source/cmIncludeDirectoryCommand.h

@@ -92,7 +92,7 @@ public:
   virtual const char* GetFullDocumentation()
     {
     return
-      "INCLUDE_DIRECTORIES(dir1 dir2 ...)";
+      "INCLUDE_DIRECTORIES([BEFORE] dir1 dir2 ...)";
     }
   
   cmTypeMacro(cmIncludeDirectoryCommand, cmCommand);

Source/cmMakefile.cxx

@@ -564,7 +564,7 @@ void cmMakefile::AddSubdirDependency(const char* subdir,
   m_SubdirDepends[subdir].insert(dependency);
 }
 
-void cmMakefile::AddIncludeDirectory(const char* inc)
+void cmMakefile::AddIncludeDirectory(const char* inc, bool before)
 {
   // Don't add an include directory that is already present.  Yes,
   // this linear search results in n^2 behavior, but n won't be
@@ -573,9 +573,17 @@ void cmMakefile::AddIncludeDirectory(const char* inc)
   if(std::find(m_IncludeDirectories.begin(),
                m_IncludeDirectories.end(), inc) == m_IncludeDirectories.end())
     {
+    if (before)
+      {
+      // WARNING: this *is* expensive (linear time) since it's a vector
+      m_IncludeDirectories.insert(m_IncludeDirectories.begin(), inc);
+      }
+    else
+      {
       m_IncludeDirectories.push_back(inc);
       }
     }
+}
 
 
 void cmMakefile::AddDefinition(const char* name, const char* value)

Source/cmMakefile.h

@@ -218,7 +218,7 @@ public:
   /**
    * Add an include directory to the build.
    */
-  void AddIncludeDirectory(const char*);
+  void AddIncludeDirectory(const char*, bool before = false);
 
   /**
    * Add a variable definition to the build. This variable