jks2pem improvements

[ehrhardt]

Thank you for the script.
Some minor changes that I hope that you like:

• dos2unix to remove the carriage returns;
• POSIX shell works fine since we have no bashisms;
• quotes to enclose the file names and support spaces on paths;
• fix a missing backslash typo;
• rm with a prompt to give the option to delete the PKCS #12 intermediate file.