configure.py: Replace 'ltx' by 'log' case insensitively

On windows the temporary filename consists of uppercase characters. This
causes that the extension does not get replaced, and the logfile is left
behind.

Checking the extension case insensitively will correctly remove the
logfile.

lib/configure.py

@@ -124,7 +124,7 @@ def checkTeXPaths():
                 inpname = tmpfname.replace('\\', '/')
         else:
             inpname = cmdOutput('cygpath -m ' + tmpfname)
-        logname = os.path.basename(inpname.replace('.ltx', '.log'))
+        logname = os.path.basename(re.sub("(?i).ltx", ".log", inpname))
         inpname = inpname.replace('~', '\\string~')
         os.write(fd, r'\relax')
         os.close(fd)