Various changes regarding resource handling:

* ResourceResolver also resolves relative URLs
* ResourceResolver also resolves absolute file URLs (if it includes the resource)
* ResourceRegistry doesn't resolve absolute paths by default (but subclasses may do)
* ResourceLookup returns resolved resources
* LiblouisTablePath: table list can not begin with hyph_*.dic
* Liblouis, Liblouisutdml & Libhyphen handle absolute file paths
New XSLT functions: louis:resolve-table, hyphen:resolve-table, tex:resolve-table
Improve zedai-to-pef 'translator' option:

* Items in the comma-separated list don't have to be absolute URLs
* Smart enough to resolve a translator based on a simple file name
* Doesn't except unknown http:// resources (fixes a security issue)