hghave: detect support for EOL in paths.

tests/hghave

@@ -23,10 +23,20 b' def has_executablebit():'
     finally:
         os.remove(path)
 
+def has_eol_in_paths():
+    try:
+        fd, path = tempfile.mkstemp(suffix='\n\r')
+        os.close(fd)
+        os.remove(path)
+        return True
+    except:
+        return False
+
 checks = {
     "symlink": (has_symlink, "symbolic links"),
     "fifo": (has_fifo, "named pipes"),
     "execbit": (has_executablebit, "executable bit"),
+    "eol-in-paths": (has_eol_in_paths, "end-of-lines in paths"),
 }
 
 def list_features():