add createprecomplete.py from m-c.
add createprecomplete.py from m-c.

https://hg.mozilla.org/mozilla-central/file/1d38626ba968/config/createprecomplete.py

escapewindow/signingscript,escapewindow/signingscript,escapewindow/signingscript,escapewindow/signingscript,escapewindow/signingscript,escapewindow/signingscript