added robustness for duplicate separators

duplicate separators previously caused issues when trying to relativize an absolute path which is needed for some tasks (e.g. links in the HTML reports, archiveArtifacts step, etc.).

src/main/resources/dsl/btc.groovy

@@ -766,7 +766,10 @@ def resolveConfig(body) {
  * In all cases backslashes are replaced by slashes for compatibility reasons.
  */
 def toAbsPath(path) {
+    // replace backslashes with slashes, they're easier to work with
     def sPath = path.replace("\\", "/")
+    // replace multiple occurrences: e.g. C://file -> C:/file
+    sPath = path.replaceAll("(/)+", "/")
     if (sPath.startsWith("/"))
         sPath = sPath.substring(1, sPath.length())
     if (sPath.contains(":"))