Poppler-0.72 replaced getCString with c_str

diff --git a/ipe-tools/pdftoipe/pdftoipe.cpp b/ipe-tools/pdftoipe/pdftoipe.cpp
index b1b8562..f62cced 100644
--- ipe-tools/pdftoipe/pdftoipe.cpp
+++ ipe-tools/pdftoipe/pdftoipe.cpp
@@ -108,9 +108,9 @@ int main(int argc, char *argv[])
   if (argc == 3) {
     xmlFileName = new GooString(argv[2]);
   } else {
-    char *p = fileName->getCString() + fileName->getLength() - 4;
+    char *p = fileName->c_str() + fileName->getLength() - 4;
     if (!strcmp(p, ".pdf") || !strcmp(p, ".PDF")) {
-      xmlFileName = new GooString(fileName->getCString(),
+      xmlFileName = new GooString(fileName->c_str(),
 				  fileName->getLength() - 4);
     } else {
       xmlFileName = fileName->copy();
@@ -127,7 +127,7 @@ int main(int argc, char *argv[])
 
   // write XML file
   XmlOutputDev *xmlOut = 
-    new XmlOutputDev(xmlFileName->getCString(), doc->getXRef(),
+    new XmlOutputDev(xmlFileName->c_str(), doc->getXRef(),
 		     doc->getCatalog(), firstPage, lastPage);
 
   // tell output device about text handling