Allow image macros to refer to other images on the server by allowing an initial /

Currently all image urls are prepended with the download path of the current page unless they start with http://

I would like to refer to other images on the server by referring to them via something like /some/other/path.

If the ImageMacro.java code checked for a leading '/' and did not compute a download path url it would allow this capability. The workaround is to fully specify the complete server path. e.g. http://someserver:8080/some/other/path. Since I'm generating this from another macro, I'd like to avoid hardwiring in the server path.

Change
if (img.indexOf("://") != -1) {

to be

if (img.indexOf("://") != -1 || img.startsWith("/")) {