RemoteFile: add FindFileList which uses the new QUERY_FINDFILE command

This adds a new FindFileList() function which will find a list of files
matching the given filename (which can be a regexp) in a given storage group
and on a specific host.

Update FindFile() to use FindFileList() and will return the first match found.

NOTE: bumps the ABI version.
MythMusic: update findIcon() to use a regexp to find the icon

This speeds up looking for an icon by replacing four lookups with a single one
using a regexp to find matching icons.
Merge remote-tracking branch 'upstream/master'