Add Norman Brandinger's suggested `-m' option in plink, to read the

Add Norman Brandinger's suggested `-m' option in plink, to read the
remote command from a local file. Advantage: you can have more than
one line in it, so you can remotely run what's effectively a small
script.

git-svn-id: http://svn.tartarus.org/sgt/putty@1010 cda61777-01e9-0310-a592-d414129be87e