Define gitfo_exists to determine file presence

When scanning the pack directory we need to see if the path
name is present for ".idx" when we discover a ".pack" file.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

src/fileops.c

@@ -53,6 +53,12 @@ int gitfo_write(git_file fd, void *buf, size_t cnt)
 	return GIT_SUCCESS;
 }
 
+int gitfo_exists(const char *path)
+{
+	struct stat sb;
+	return stat(path, &sb);
+}
+
 off_t gitfo_size(git_file fd)
 {
 	struct stat sb;

src/fileops.h

@@ -31,6 +31,7 @@ typedef struct {  /* file io buffer  */
 } gitfo_buf;
 
 
+extern int gitfo_exists(const char *path);
 extern int gitfo_open(const char *path, int flags);
 extern int gitfo_creat(const char *path, int mode);
 #define gitfo_close(fd) close(fd)