(svn r10143) -Add: store the filename of the grfs opened and allow easy access to the name

-Codechange: store the SpriteID in the spritecache too
-Add: add a PNG loader for graphical files
-Documentation: added a document to explain the PNG format

projects/openttd.vcproj

@@ -1007,6 +1007,12 @@
 			<File
 				RelativePath=".\..\src\spriteloader\grf.hpp">
 			</File>
+			<File
+				RelativePath=".\..\src\spriteloader\png.cpp">
+			</File>
+			<File
+				RelativePath=".\..\src\spriteloader\png.hpp">
+			</File>
 			<File
 				RelativePath=".\..\src\spriteloader\spriteloader.hpp">
 			</File>

projects/openttd_vs80.vcproj

@@ -956,7 +956,7 @@
 				>
 			</File>
 			<File
-				RelativePath="..\src\newgrf_industrytiles.h"
+				RelativePath=".\..\src\newgrf_industrytiles.h"
 				>
 			</File>
 			<File
@@ -1563,6 +1563,14 @@
 				RelativePath=".\..\src\spriteloader\grf.hpp"
 				>
 			</File>
+			<File
+				RelativePath=".\..\src\spriteloader\png.cpp"
+				>
+			</File>
+			<File
+				RelativePath=".\..\src\spriteloader\png.hpp"
+				>
+			</File>
 			<File
 				RelativePath=".\..\src\spriteloader\spriteloader.hpp"
 				>
@@ -1636,7 +1644,7 @@
 				>
 			</File>
 			<File
-				RelativePath="..\src\newgrf_industrytiles.cpp"
+				RelativePath=".\..\src\newgrf_industrytiles.cpp"
 				>
 			</File>
 			<File