Add distinctive prefixes to tempfiles to aid finding resource leaks.

src/ZODB/Connection.py

@@ -1247,7 +1247,7 @@ class TmpStore:
             ):
             setattr(self, method, getattr(storage, method))
 
-        self._file = tempfile.TemporaryFile()
+        self._file = tempfile.TemporaryFile(prefix='TmpStore')
         # position: current file position
         # _tpos: file position at last commit point
         self.position = 0

src/ZODB/ExportImport.py

@@ -34,7 +34,7 @@ class ExportImport:
 
     def exportFile(self, oid, f=None):
         if f is None:
-            f = TemporaryFile()
+            f = TemporaryFile(prefix="EXP")
         elif isinstance(f, six.string_types):
             f = open(f,'w+b')
         f.write(b'ZEXP')

src/ZODB/utils.py

@@ -251,9 +251,9 @@ def get_pickle_metadata(data):
         classname = ''
     return modname, classname
 
-def mktemp(dir=None):
+def mktemp(dir=None, prefix='tmp'):
     """Create a temp file, known by name, in a semi-secure manner."""
-    handle, filename = mkstemp(dir=dir)
+    handle, filename = mkstemp(dir=dir, prefix=prefix)
     os.close(handle)
     return filename