XProcSpec loads the Calabash extension library

Hi,

I had trouble last week with my XProcSpec testings. Reason was that @ndw moved it's calabash library `http://xmlcalabash.com/extension/steps/library-1.0.xpl` on his web server (see https://github.com/ndw/xmlcalabash1/issues/353). At the end I found out that the real problem was in XProcSpec:

> Ok, my issue had multiple levels. One of it was that I'm using [XProcSpec](https://github.com/daisy/xprocspec/) and that is [trying to load each imported XProc file](https://github.com/daisy/xprocspec/blob/release/1.4.3/src/main/resources/content/xml/xproc/preprocess/preprocess.xpl#L176) using p:load. Calabash does the magic [of redirecting the extension library URL] only for the p:import - not if you try to load . But that is ok, I think.

For now it is fixed as - thanks to @ndw - he moved the library back to it's origin place. But to get stable and undependent results (undependent from external http requests) I think XProcSpec should ignore ``s pointing to the Calabash extension library, shouldn't it? Another way could be to redirect the HTTP requests by an internal catalog.