CLJS-683: :source-map-path option

Source map paths to source files can now be made relative to anything
making integration with web work flows simpler.

src/clj/cljs/closure.clj

@@ -762,6 +762,7 @@
                     {:lines (+ (:lineCount sm-json) 2)
                      :file (:file sm-json)
                      :output-dir (output-directory opts)
+                     :source-map-path (:source-map-path opts)
                      :relpaths relpaths}))))))
         source)
       (report-failure result))))

src/clj/cljs/source_map.clj

@@ -152,13 +152,13 @@
             [] cols)))
       [] lines)))
 
-(defn relativize-path [path {:keys [output-dir relpaths]}]
+(defn relativize-path [path {:keys [output-dir source-map-path relpaths]}]
   (cond
     (re-find #"\.jar!/" path)
-    (str output-dir (second (string/split path #"\.jar!")))    
+    (str (or source-map-path output-dir) (second (string/split path #"\.jar!")))    
 
     :else
-    (str output-dir "/" (get relpaths path))))
+    (str (or source-map-path output-dir) "/" (get relpaths path))))
 
 (defn encode
   "Take an internal source map representation represented as nested