Implement plain view

This implements a way to access plain blobs by path (similar to the
tree view) instead of by sha1.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.c

@@ -187,6 +187,7 @@ static void prepare_context(struct cgit_context *ctx)
 	ctx->page.mimetype = "text/html";
 	ctx->page.charset = PAGE_ENCODING;
 	ctx->page.filename = NULL;
+	ctx->page.size = 0;
 	ctx->page.modified = time(NULL);
 	ctx->page.expires = ctx->page.modified;
 }