Support Eclipse IDE / EGit

[JBlaufussTR]

The Eclipse IDE's git provider (EGit) supports S/MIME (X.509) signatures using an external gpg, but smimesign does not support several of the command-line options it uses (they are supported by gpgsm), so it does not work with Eclipse.

Please update smimesign to support the needed command-line options in a way that is compatible with gpgsm, so that it is compatible with Eclipse EGit.

See the issue I opened in their repo for details: eclipse-egit/egit#59.

Thank you.