make nsis script use local plugins

[RoDuth]

Ghini/ghini.desktop#109

[mfrasca]

this doesn't yet address forcibly installing in virtual environment, in case corresponding egg is available as a system-site-package.

[RoDuth]

from memory you, as I had done at one point, had installed py2exe from the sourceforge installer. These only work on the global install and hence you would have had to install all the dependencies globally also, as I had done also. I feel this does not seem like a common scenario if someone is following the instructions and using standard practices (virtual environments). Could try using this I guess but that seems like it would be a pain for all subsequent runs of the script. I have mentioned this approach in the documentation on the 'py2exe will not work with eggs' section. I think if someone was looking to troubleshoot this rare issue that should be enough. Or maybe another dot point mentioning the possibility of globally installed eggs. I much prefer to keep the script simple as it is only there for convenience.

[coveralls]

Coverage decreased (-0.009%) to 65.825% when pulling 1bdd818d0af30036b0662e1d5cd9f1585407419e on RoDuth:ghini-1.0-dev into fdf95d48e29784c7a79e8375b45c5d3b5ed56af9 on Ghini:ghini-1.0-dev.