Fix source locations when recompiling from an xref buffer.

From slime/slime#175

* sly.el (sly-recompile-locations): pass full filenames to
swank:compile-multiple-strings-for-emacs

(cherry picked from SLIME commit
0249a079921b29ceb720c6524c30a7ee8d60a848)

Conflicts:
	ChangeLog
	slime.el

sly.el

@@ -2573,7 +2573,7 @@ ASK asks the user."
                              (sly-current-package)
                              start
                              (if (buffer-file-name)
-                                 (file-name-directory (buffer-file-name))
+                                 (sly-to-lisp-filename (buffer-file-name))
                                nil)))))
         ',sly-compilation-policy)
     cont))