Allow '-' as an alias for stdin

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This is a bug report from Debian, see 
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=520305 and if possible 
include 520305-forwarded@bugs.debian.org in any follow up correspondence.

the freebsd port of the pssh toolset has been modified to allow '-' as an alias 
for stdin in the host file specification 
(http://www.freebsdsoftware.org/security/pssh.html).  this feature is included 
in other tools (e.g., fping) and is very useful in them.  could it be 
implemented here?

Original issue reported on code.google.com by and...@pollock.id.au on 12 May 2014 at 12:13