Fix nightly sendmail call arguments for multiple addresses.

On cygwin, the mailer program is "email" instead of "Mail". "email" requires
multiple recipient addresses to be comma delimited instead of space
delimited. Update "nightly" script to comma delimit the addresses when using
email program.
Merge pull request #538 from thomasvandoren/fix-nightly-recip-on-cygwin

Fix nightly sendmail call arguments for multiple addresses.

On cygwin, the mailer program is "email" instead of "Mail". "email" requires
multiple recipient addresses to be comma delimited instead of space
delimited. Update "nightly" script to comma delimit the addresses when using
email program.