Adds support for utf paths on Windows.

Not all file formats/calls are supported yet. It will be expended.

Please from now on use BLI_fopen, BLI_* for file manipulations.
For non-windows systems BLI_fopen just calls fopen.
For Windows, the utf-8 string is translated to utf-16 string in order to call UTF version of the function.

source/blender/imbuf/intern/targa.c

@@ -268,7 +268,7 @@ int imb_savetarga(struct ImBuf * ibuf, const char *name, int flags)
 	if (ibuf->planes==32) {
 		buf[17] |= 0x08;
 	}
-	fildes = fopen(name,"wb");
+	fildes = BLI_fopen(name,"wb");
 		if (!fildes) return 0;
 
 	if (fwrite(buf, 1, 18,fildes) != 18) {